Been there, done that and got the t-shirt x 2. Literally.
Rural France, between 15 and 20 people every day for 2 weeks, 8 bedrooms plus four in a friend's house. AMA. 🤓 Not gardening or building work but an independent film project where my house was the location and set, but also served as accommodation for the cast and crew and I was the sole caterer. There were three couples (me and DH, plus 2 of my adult children and their partners) but everyone else needed their own bed. There was a revolving door of people who came and went mid shoot, so I had to keep changing bedsheets and towels and the sleeping arrangements were constantly re-jigged depending on who could share and who couldn't. We paid a friend nearby to provide some overflow accommodation at night, but all the catering was done at my house.
I made all the mistakes and learned the hard way so you don't have to.
Firstly, don't underestimate how hard this will be on you. For me, the first two or three days felt like a fun challenge and all the rest after that felt like I'd died and gone to hell. I've never been so exhausted and stressed in my life. You won't have time to do anything except shop for and prepare food and clear up from food, and stress about keeping food either hot, or cold, three times a day. Even with someone helping you to clear up and load the dishwasher, if you want to feed them well and not get too repetitive or boring, it will be a full time job.
In my case, I wasn't being paid for use of my house as a film set and I wasn't saving any money personally by doing this. The film was written, directed and produced by two of my adult children and the use of the house with accommodation and catering was our gift to them as they were self financing the whole thing on a tight, but still substantial budget. It was actually costing me quite a lot of my own money so I did have to be mindful of the cost. Food in France is incredibly expensive, especially fresh fruit, veg and meat, and not always as good as people might expect unless you can afford to not worry about the cost at all and buy the best of everything. Finding things that you might use at home as a convenience or short cut is not as easy as in the UK. I imagine it's similar in Spain?
In my situation although my children and their partners were involved, everyone else was a paid professional who was actually working on location, so I felt the pressure to make sure it was of a decent standard. So many people had offered well meaning advice about 'keeping it simple' and 'just give them baguettes and meats and cheeses for lunch' without understanding the specific challenges I was up against. A pack of four decent quality slices of ham costs around 6 euros in my local supermarket in France, and one big, hungry man could demolish that in a sitting. I couldn't just bung everyone a 'Chicken Tonight' casserole and a pouch of microwave rice every night. Not that I would do that anyway, not my style, but it was neither practical nor affordable to do that, even if I'd wanted to. A jar of half edible casserole sauce alone would be about 4 euros in France and with all the big strapping men I was feeding I'd have needed one between two and a pouch of rice each, and that's before the chicken or any veg.
Due to the numbers involved and the fact that they all needed to eat at exactly the same time, it wasn't practical to do much in the way of pasta, or chips or omelettes, or other easy/cheap things. So I cooked virtually everything from scratch in bulk and in advance wherever possible. And I had to have two choices, often three, because of dietary restrictions, allergies and a bloody vegan.
It's great that you thought of a cleaner. I wish I had done that. I left everyone responsible for their own shared bathrooms and their own laundry. Luckily we have a second washing machine in an annexe property outside of my main house. But I still had a ton of sheets and towels to deal with once they'd left. I provided all the relevant laundry and cleaning stuff for them to use as they wished, but I probably should have checked the bathrooms more than I did, or paid someone to do them. By the end they were not pretty...
Breakfasts: I kept it simple and let people sort themselves out. Supplied several types of cereal, milk, multipacks of yogurts, bananas. Cartons of fruit juice, fresh fruit. We got through tons and tons of bananas. Sliced bread and butter for people who wanted to make their own toast, jams/peanut butter etc, and I went to the supermarket daily for baguettes. I bought bags of frozen croissants and baked them at home as buying them fresh each day for that many people would have been eye wateringly expensive. Not everybody even bothered with breakfast but others ate loads.
As you have fewer people, you could boil a load of eggs and offer those, or include some sliced hams and cheeses, but I didn't do this for breakfast. It would have added significantly to the already huge cost and I had very little help in the kitchen (DH was busy with other tasks, but helped where he could) so I didn't have time.
I supplied a kettle and teabags and a Nespresso machine with unlimited pods and put it on a table outside of my kitchen so they weren't all under my feet while I was trying to prep lunch, which started more or less as soon as I got up and dressed. My God, did they get through a lot of coffee pods. One bloke I swear must have drunk 10 or 12 double espressos a day. He was Serbian. Apparently that explains it...
If I were to do it again which I won't ever not even if my life depended on it I would ration the pods, because of the relentless pressure to keep going to the shop every five minutes for essential things we ran out of. In rural France that's no joke. But in your case it's a bit different. They are doing you a favour, so you might feel less inclined to ration anything.
Water: Our water is drinkable and we decided against a constant supply of bottled water for everybody, not because of cost but because of the practicalities of trying to keep so many people supplied with endless cold plastic bottles of water and the amount of space it took up in the car when we went shopping twice a day. and the fridge space and the constant recycling runs.
We bought ONE lot of 500 ml plastic bottles for everyone and wrote name labels on them. When they were empty people could refill their own bottle from a constant supply of filtered tap water kept in water jugs in the drinks fridge. It was easier to keep the jugs constantly replenished and cooled than to keep restocking the fridge with endless plastic bottles. The labels also meant that when people put their bottles down, they always knew whose was whose. Maybe buy a borrow a big Eski cooler for drinks and ice, as you will run out of fridge space, even if you think you have loads. You need to keep your food cool as well and drinks take up so much space.
I had particular challenges that you hopefully won't have, like not being able to clatter around in the kitchen at certain times because the cameras were rolling nearby and I couldn't make a noise. And loads of my stuff had been moved around to different parts of the house because of where they were filming, so I was constantly moved around to do my food prep, then moved back again and couldn't find half the things I needed. It was really stressful.
I couldn't stagger the serving times, everyone on a film set breaks for meals at the same time, it's a really tightly controlled filming schedule, so I had to have it all ready and dished up exactly when they were ready. Cooking dinner more or less from scratch for so many people in an ordinary domestic kitchen when you've barely had time to clear up from lunch....uurgh. You can't cook rice or pasta or roast potatoes for 20 people in one go, so then you have the challenge of trying to keep things warm while you finish the next batch. And it was SO hot, but I couldn't have the kitchen door open very often.
I could write an essay and I practically have on all the things that made my situation particularly challenging, but hopefully they largely won't apply to you.
As I said, I tried not to fall into the trap of just bunging everyone a lump of baguette with ham and cheese every day, for various reasons it wasn't appropriate and these lot were HUNGRY. I couldn't give them bread and things for breakfast and then more bread and things for lunch. They needed proper meals with variety. But we did sometimes have things like giant sausages and fried onions in baguettes. Quiches and huge frittatas made in big foil trays and salads, breakfast burritos (for lunch) which I made and froze in advance then put in the air fryer. Homemade falafels in wraps with hummus and pickles. Jacket potatoes with tuna mayo, coleslaw, cheese and beans. Macaroni cheese. Big trays of roasted chicken pieces with a range of nice salads.
Things that will make your life a million times easier: Disposable foil trays for anything roasted or greasy, or anything in a sticky marinade that burns and is particularly horrible to wash up, or big roasting dishes that won't fit in the dishwasher. Just use foil trays and chuck 'em. Air fryers - I needed two, you might be okay with one, but two would be better. A big slow cooker. A rice cooker. A pressure cooker or Ninja multi cooker thing. Pressure cooking loads of either soft or hard boiled eggs is a breeze and they peel really easily. No worries over timing. Just set it and go. Perfect every time.
For lunch I often resorted to paper plates and disposable 'street food' type bowls where possible, because there was only me clearing up. By the time I'd loaded the dishwasher with cooking stuff there was no room for plates, and there would still be a second load of pots and pans waiting to go in once the first load had finished. But I drove over with all this disposable stuff in the car which I'd bought from Makro, you might be flying over?
You will need loads of freezer space. If you don't already have it then buy or borrow a big freezer. Cook and freeze as much in advance as possible. I did some lasagnes, curries, chillies, a beef and a chicken casserole etc so I only needed to worry about the rice/salad/veg or whatever, on the night. But with 20 people for two weeks there was only so much I had room for. Once the frozen stuff was used up I never had the time to cook 'in advance for the freezer' because I was too busy cooking for what was needed for the next meal.
I had some great meals that went down really well and were reasonably easy to do that didn't break the bank, so ask away if you need ideas. The other thing I did which turned out to be a great idea was supplied things like tinned ravioli and pot noodles for people to help themselves if they were hungry late at night or between meals. If you have young, strapping men on this project and they are working hard, do NOT underestimate how permanently hungry they will be.
Sorry that was so long.