Without knowing a bit more about your circumstances the answer is going to be of the 'How long is a bit of String' variety.
What kind of a job, where in Geneva is the company/bank/office based, is it a local contract or a company transfer from abroad with simply oddles of financial help with the move?
Geneva is expensive, housing is generally in short supply and it's not going to be a question of simply deciding that you'll be living outside the city 'near a good school'.
If you're staying for a while and are putting them into the state system they'll go to the nearest school, you really don't get to chose. State schools are pretty good by the way and in Geneva they start at four.
If you can afford a private one then living near to the one where you've managed to get places is also not always as easy as it sounds.
Popping back to the UK is easy, Easyjet flights from Geneva go to various London airports several times a day, at least once a day to Manchester and (I think) a few other major airports. But school term times are strictly adhered to, you won't get away with taking the children out of school for any extra days without a good excuse; and a family holiday is not an acceptable reason.
Ask at any upcoming interview if relocation services are going to be offered as part of the package (help with finding long-term accommodation, school fees if you're going private, heath insurance contributions, etc.).
Be aware that these 'perks' will be taxable as they're considered part of your salary, and are often refundable to the company if you leave within a certain time frame.
Do not sign anything to do with a work contract, accommodation, insurances, etc. without getting either an official, written translation or at the very least all of your questions answered in writing.
There are private relocation companies, but they won't be cheap; nothing here is!
I'm sure there are loads of threads on this subject already on forum that will answer many of your general questions.... Longbyt has already linked to a recent one. You could try putting a few key words into the Search engine and see what you can find that way.
I'm told there's a lot of useful information in the 'Stickies' but must admit I've no idea how to find them. Perhaps a Mod could help here?
Also; I'd suggest you also try joining this forum; http://www.glocals.com/geneva/
Although EF is truly wonderful for a lot of things there are very few of us Geneva based members here, sadly most of them live in the germanic part!