I think, regardless of any fall out after SIL holiday, you should call a family meeting of all owners over the winter to agree ground rules going forward.
Basic levels of essentials that should always be left stocked when visitors leave. So toilet roll in each toilet and at least 4 more in the cupboard, a roll of kitchen towel in the kitchen and at least 1 in the cupboard, cleaning supplies…from basic condiments through to basic staples like “enough pasta and rice for 1 dinner each”….
An agreement - not necessarily on using the cleaner during a stay - but that all occupants pay for the cleaner to come in when they leave so the house is properly clean for being left empty and for new arrivals.
What to do about laundry - does the cleaner sort that (might increase her fees to do that), or should occupants wash and dry the sheets on departure? Is there a second set so each bed can be left fully and freshly made for new arrivals?
Same with towels?
Is it worth spending a little money on some storage containers for the kitchen for keeping staples safe while the house is empty - and also allows you to say “the rice and pasta jars need to be left at least half full” or whatever? I would go for see through plastic or glass cannisters to easily see what’s inside, things like rice, pasta, tea, coffee, sugar, maybe flour or anything else you want to keep.
Be clear that people can use anything in cupboards but the expectation is that they are replaced (like for like) before they leave.
Consider if you want different rules on alcohol, or if you want a small locked cupboard for your own alcohol. So your nice bottle of gin isn’t drunk and a cheap bottle from Lidl/Aldi left to replace it.
Separate to the general rules on what to do/not do while staying, it gives a chance for everyone to talk about what they want from the house and how they want to use it. And that includes discussing how both short term maintenance (cleaning shower traps/drains, emptying bins etc) and longer term maintenance (annual cleaning of gutters, washing of windows, preventative maintenance needs, and what to do if something breaks or a tile blows off the roof in a storm…) - the longer term includes things like occasional painting, oiling of locks/window mechanisms so they continue to work, etc. How will it be decided what’s needed, schedule to get things done, to DIY or pay for locals to do the work, how to share both the work and the costs involved etc. can all be discussed in that conversation.
And also things like - if the iron breaks…does the visitor replace it, or tell a designated person who is the main “manager” of the property so that it can be replaced …may depend on what’s available locally and the quality of what you want there. But things like plates and glasses (do you want matching sets, or need to make sure there’s enough there for next arrivals), broken deck chair for outside, blown light bulbs, torn picnic blanket…
This is not something to do this week. For sometime over the winter - tell them beforehand what you want to talk about, to make sure there are no problems and to make the use of the house enjoyable for all its owners, not a burden on you all. (Even if the burden currently mainly falls on only a few of those owners..).
And coming out of that meeting, there should be an agreed set of rules - which get written up and formally shared with everyone afterwards. And the short term rules related to the ongoing use of the house (cleaning, levels of stocks in cupboards, anything about “no wild parties outdoors after midnight because of elderly neighbour”…type sensible things, and phone numbers of important contacts like local cleaner and handyman) should be shared by email but also printed out and laminated to leave in the cottage where ANY visitors can be aware of the “house rules”.
It might also be helpful to set up an online logbook - where any visitors can post any problems or issues they see, some may need immediate attention but others could be discussed at the annual discussion (a few people noticed that the wind on 1 side is very strong but that a windbreak in a certain point could make it a lot better…so is it worth doing that and who will organise it and how to split the costs fairly, for example).