"I want to set up a broadband system that can be shared between 3 holiday cottages." -- That is very likely to be contrary to your terms and conditions, which will normally specify that you cannot provide your ADSL connection to others outside of your own household, or a similar clause along those lines.
And yes, it impossible (as far as I am aware*) to allocate IPs without having control over the clients. They will have to remain dynamic. There should be no problem with using access points, though, so at least that part of your plan will work.
*Home/small office equipment.