From my vague recollections when the tax accountant explained it to me, the capital gains thing only kicks in after a certain amount of years (10 years, I think, don't quote me on that) and if you move back in before the ten years it cancels it out. Also you have the house valued at the start of the capital gain period (like, at the 10 year mark) so the gain you pay is only on the increase in value from that time (and not when you first bought it).

It's worth getting some advice from an accountant before you proceed to clarify all of this.