To tell my mum I’m not taking her on holiday again?

I agree with this 100%.
You don't have to make an announcement.
Just don't arrange another family holiday together and if she mentions anything just say the 1st time around wasn't a good experience.
Your mom does appear to be lonely so maybe arranging some days out with just you and your mom could bea better idea rather than a holiday away.

Do a separate weekend just you and her next time.

I'd be the granny in this situation. And there is NO way I'd want to be with family for every minute of a holiday! I'd actively be wanting time on my own. A book. Scrolling on my phone. Relaxing (napping) in the sun. And I'd also realise expecting my DC to spend time with me exclusively and restricting what the children could do because of it was unfair.

I don’t see why you need to make a bug announcement - if you don’t want to go on holiday again with your DM, then don’t. When you say “doing some things together and some apart” - what exactly did you have in mind? As far as the beach is concerned, did your DM not want to go, or did you not want her to go? If one of your DC is 18, did they not want to do things on their own sometimes? It’s difficult because your DM is on her own - she probably expected to be included in “family” activities. It’s not reasonable of her, though, to prevent you from doing things with your DC because she neither wants to take part in the activity, nor be left on her own.

I seem to have spent the week looking after mum. she wants me to go everywhere with her, carry things, get her drinks, help her getting changed for the pool, sort her medication and check menus for her.

This sounds tough on you and of course Yanbu as this is your holiday too.

on the fourth night she told another couple at dinner “I don’t know why she’s brought me if she’s going to leave me on my own all the time.” I spoke to her and she said I promised her a holiday and have barely spent any time with her. but I’ve spent nearly every evening sitting with her instead.

This suggests you have left her alone all day and just spent evenings with her ?

my 18 year old said that he doesn’t want grandma coming on holiday again because “she makes you miserable and then you shout at everyone

Why are you shouting at everyone?

As someone who includes elderly parents in family holidays, it's a great opportunity to spend time together but you can't treat it as a normal family holiday, dealing with intergenerational needs is tricky and it looks like this hasn't been considered. Can you not adapt some of your daytime activities to include your mum but if she has come away and spent the first 4 days waiting for you to return from the beach or activities, it's unsurprisingly she is not enjoying and it's not working.

You all are staying in one room??

No need for any announcement, just don't ask again. A weekend away with just the two of you might be something to consider in future, not the traditional week in a resort.

I am not far off your mum’s age, significant health issues.
The last thing I would want is anyone on a holiday having to ‘sit’ with me while there are other things to do, especially with kids involved.
Yes, it’s a bit shit when your body won’t do what it used to but you must accept it and work with it.
So for me I’d be sitting by a pool with my Kindle. iPad in my room for a few films. Some family time at meal times, and then maybe a few hours here and there where someone might spend time with me.
What I wouldn’t do is emotionally blackmail a loved one it’s not fair, especially on a holiday.
If she can organise her meds at home, she can do it on holiday.
I am not being cruel, in fact I totally get where your mum is at physically.
It is not just about the holiday. If she’s behaving like this now at 63 she could be around another 20 years and her demands will increase when they don’t always need to.

I can’t see why you need to announce it, just don’t take her again. Doesn’t sound like she’s enjoyed it either so she may not even want to come again. Being able to manage on her own in her own home and routines is different to a pool side holiday though and I think it’s understandable she needs a bit of extra help. Yourmother isn’t to blame for your behaviour though, shouting at everyone and being so moody that it’s upsetting your kids is on you. I think your mum sounds like she’s been far needier than necessary but I think there is wrong on both sides here and I agree this holiday is better as a one off.

Considering she is able, I think your mum has over relied on you during the holiday, but I don't think she's unreasonable to imagine she'd be included in your day-to-day activities within her capacity, of course; otherwise, what's the point of her being on holiday with her family.

I don't think you can tell her you won't be holidaying together again, based on her expectations. But I'm not sure how you do tell her that she won't be joing you again. Not an easy one.

If she has mobility issues then you can’t really leave her alone. You should have thought it through before inviting her. I think you were just frustrated at spending all your time with her and missing out on the kids. I think perhaps go away for a few days with her one to one, and save your big holiday with your husband and children. I think it was too much responsibility for you and meant your husband was flying solo for most of the holiday with the kids. I do get it as my father is blind with Mobility issues and can’t be left alone somewhere that’s not his home. It’s draining being a carer and does take your time away from your family. 🌺

Agree it just sounds like a clash of expectations. These things happen sometimes in multi household holidays. Wouldn't have killed the 18 year old to go to the bar for her or check the menus either, if she really couldn't do those things herself.

If you want to go away with her again, I agree with the PPs who've said a weekend just the two of you makes more sense. And have some discussions about what's expected beforehand. In particular I'd want to be clear that she's aware she'll need to do the things she's capable of doing. For example you mention her wanting you to sort her medication. Does she not do that herself at home?

Totally understand why you would feel like this but I'd give you mum a chance and explain to her everything you have just said here.
Including son.

She geuninly may not realise and also she maybe desperate for care, extra care having that other person around gives.

After that decide and set firm boundsires.

From her point of view though you’ve all gone on holiday together as a family and then you don’t want to do stuff with her. It’s not weird that she didn’t predict that. Totally understandable that you want to go to the beach sometimes, but she’s left out because of mobility and that must be a bit rubbish.

Are you all in the one family room? You, partner, kids including an 18 year old, mum in her 60s?

Im surprised anyone wants to spend time with anyone tbh.

63 isn’t elderly. I’m 60 and work full time (fully expect to do this until 67), regularly walk over 10 miles, gym with weights and cardio 3 times a week. I don’t run anymore because it makes my knees sore, but that’s my only limitation. I’m not unusual for my age either. I would class 80 as elderly as most of the people in their 70s that I know are still pretty active.

I would assume therefore that the OP’s Mum suffers from particular health conditions not directly related to her age. She seems to manage well in day to day life though, and should have been equally capable when away on holiday. If she doesn’t need 24/7 care at home, she doesn’t need it on holiday. She seems to have expected to be OP’s sole focus and this is just unreasonable. I wouldn’t take her on holiday again either.

Book the next holiday and tell no one apart from your husband until the last minute. We dont invite my parents or in laws otherwise it becomes expectation every time we go away with our children and it isn’t relaxing at all and harder work than if we just went with our kids. We keep our holidays as a surprise for our children also x

I agree that sharing a hotel room is highly inappropriate both for your mum, your husband and your 18 year old son! This has been poorly thought out and you need to learn from this and see how you can adapt to include her.

Go to the pool half a day and beach for half a day, go for a coffee and cake together but try to break up the day and make it more inclusive

This. Why do you feel that you need to explicitly tell your mother right now that you won't holiday with her again, OP?

I assume it's a stress response. But agree, no decision needs to be made now and it certainly doesn't have to be communicated.

OP as you still have one more day, is there time to communicate some kind of plan that might make everyone feel a bit more secure? Managing this stuff off the cuff is always tougher. Like if you said to DM, we're going to the beach after lunch and I'll help you to a seat by the pool first. Tell me now if you will need anything doing first. Then we can all go for a meal and watch the entertainment/go to the pub over the road in the evening.

No, I wouldn’t, not unless she makes that conversation impossible to avoid

My DM was older when this became a possibility but we took her on a couple of family holidays and it then became clear that these holidays couldn't be all things to all people, particularly when her mobility got worse.

What I used to do was go away for a few days with my mum on our own and also have a family holiday without DM. We did get on very well though in general. Don't burn your bridges.

Slightly off track, but your brother lives in Scotland, why can't she go and stay with him, depending on where it is. It's his turn next time.

What a stressful holiday! Dont take her again but don’t state that you won’t. Try not to regret anything, just move on with lessons learned.