Just read this thread. It is the loveliest I've ever read on MN. Your kittens and gorgeous; you're amazing, 3 weeks of broken sleep, 2 hr feeds, constant care and attention. Amazing. They are beautiful though aren't they?
I just thought I'd mention kitten food by James Wellbeloved. Mostly, the kitten food you get in the supermarket is OK for kittens from about 8 weeks, but can often play havoc with their tummies until they get used to it; they're generally fine with it at 12 weeks.
We've had 3 kittens in the last 5 years. When we first got each of them, they each found 'normal' kitten food too rich and wound up with diarrhoea and farts to die for - really, really good farts, farts a 12 year old boy would be jealous of!
The Wellbeloved stuff is less demanding for little kitty tummies. You can get over the internet (eg. here), but your friendly Pets at Home probably have it. A bit more expensive I think, but you don't need it for long, just while they get used to having solids in their tums; I don't think we ever used it for longer than two weeks.