So far, I'm thinking:
Beds: at least one (probably two) zip links which can be superkings. Good pocket sprung mattress, topped with comforter and waterproof protectors for peace of mind. Then sheets, obviously.
A combination of feather/down duvets and non allergenic throughout the house. With a couple of spares to allow for extra options.
One feather/one foam pillow per guest with a spare (equal ratios) of one per two guests.
Nice blankets (wool) and throws for each bed and sofas.
Blackouts in bedrooms.
Kitchen needs good quality but tough kitchenwear (1.5 to 2 of everything, including different types of glassware/china). All the cookware needs to be sized to deal with a party of ten.
Appliances need to be full set (oven - actually we have Aga and twin oven alternative - dishwash, washer dryer, fridge and sensibly sized freezer)
Sofas - all nice fabric three seaters. We have two sitting rooms, one of which is more adult (very glam 18th C plasterwork and large open fire). Both will have two big sofas and extra armchairs. Only one will have big family TV so the other can be quieter for reading/cocktails etc
Garden furniture and toys. Not loads but enough to give kids a thrill of novelty. Maybe also some books and boardgames but not everywhere
Disposables - enough to get you out of most problems at least for the first couple of days.
Coathangers, mirrors, coathooks.
Baby related stuff. To be stored when not needed.
And no dogs!