Have worked a long time in the Middle East and the last time left the Charter World to do it. Never looked back!
ott - Given the uncertainty of the charter world you really don't, IMHO, have much of a decision to make. By moving to EK you will be making a quantum leap for you and your family that will remain with you for the rest of your lives. Dubai is a great place, only 7 hours from EGLL, EK are a good and expanding airline. Your kids will benefit from an excellent education and if you send them to board in the UK, when they are old enough, they will go to quality schools you could only dream about if you stayed with Charter. Wives, generally, (but not always), prefer the ME to the Far East. As an expat. your social life is usually far more interesting than the UK, (my experience, anyway).
I found that going long-haul in the ME was far less tiring than Charter in and around Europe, yes, a few days away followed by some quality time off with the family in a place where you can really make use of it. The temperature does go to the high thirties/low forties, on average, for four months but your family will acclimatise.
Financially you won't look back and will eventually retire much further up the financial tree.
If you find that after five or ten years you want to go back then you can and still get a job, but don't expect Emirates to still be making you offers to join them in five or ten years time!
If you can correspond with people now working for Emirates who have been there long enough to make an objective assessement it would be all the better.
Best of Luck.