Hi Gillian, sorry it has taken me so long to get back to this thread.
We don't live on an island now but live in a fairly isolated community which is probably akin to were you are going in terms of facilities.
Things to consider - what kind of person are you? If a mooch round the shops, a meal out, a takeaway, trip to the cinema is your ideal way to spend your free time, then you will hate it. If your kids are used to lots of varied after school activities then they won't like it either. Although these things may sometimes be available, the choice will be limited and in order to enjoy that kind of lifestyle you have to be prepared to look to yourselves for ways to fill your time - eg cycling, swimming (if near a pool), library, take advantage of whatever is offered locally.
On the plus side, sense of community is generally very strong. I have lived here in Ardgour for about 15 months now and have made a lot of good friends - just get involved with what's going on and you soon get talking to people - unlike bigger cities people are generally interested in making time to find out about you and welcome you (IME).
Your kids are at an age where they haven't got to the stage of being dependent on lots of extracurricular activities so that would work to your advantage. We have been insistent with our two dds that they learn how to amuse themselves (hobbies etc) rather than expecting things to be laid on for them, and it seems to have worked - there isn't an awful lot to do here but they are never bored.
Shopswise - expect to find it difficult to get things like kids shoes and maternity clothes, fancy foods like sun-dried tomatoes etc, and during the winter you might find yourself cut off from the mainland (or yourself stuck on the mainland) when the boats can't sail so you need to think ahead and stock up on food etc (we found a huge freezer was essential when on our little island). Internet banking is advisable. Food will be more expensive there too, and you will clock up expenses in travel and b&b to get to the mainland which needs bearing in mind.
Tbh I think that if you prepare your kids well then living in an isolated community is no bad thing. There are lots of teens round here and they are all content with life (that's from talking to both them and their parents).
Anything else you want to ask, feel free!