Just a precaution--I know you don't intend to breed your kittens, but it happens often enough without people intending it that I figured I'd better say something:
Kittens can have kittens as early as 5 months old (some reports of 4 month olds). This is before the traditional 6-month neuter date!
If your cats are purebred and you wish to breed them when they are older, you will unfortunately have to keep them separate when they are not being closely supervised, as it only takes a minute for the deed to be done, and small cats do not do well during pregnancy and birth.
If your cats are not going to be bred, then I suggest finding a vet who will neuter them early--female first, if you don't have the money for both right away (because the male will still be fertile a little time after his neuter--but don't delay on him, either, since males tend to spray). Early spay/neuter is becoming more and more common, and is quite safe. A vet who normally waits until six months may be brought around by your telling him that you have two intact kittens in the same household, and do not want a dangerously early pregnancy.
Good luck; and (hint, hint) we love pictures!! Got any of your precious pair?