Kittens farts smell of egg

[DarcieStarlight]

Wondering if anyone on here can help first rather than paying a fortune at the vets if it's a simple problem!
I've got 2, 10 week old kittens. (They are beautiful)! Twins too which is apparently rare in cats! (Or so I'm told)
Anyway, one of them farts a lot. Can never hear it but my god can I smell it. They smell of rotten eggs and it usually starts about teatime on an evening and goes on for most of the night. If he's laid next to me I literally cannot cope with the smell I have to get up and move away. If I leave the room and come back in he has the capacity to stink the whole place out.
He's weeing and pooing normally, (solid poos not runny) he eats and drinks plenty and he plays and appears to be in good health.
When I first got them 2 weeks ago they both had gunky eyes and were full of cold sneezing all th time and runny noses, so I had to bathe their eyes a few times each day and they seem to have cleared up perfectly well.
Is it something as simple as food or does anyone know if this is some form of medical condition I would need to take him to the vets for.
The other one is fine so I'm thinking that it may not possibly be the food!

[JorisBonson]

Kitten farts are THE WORST. My boy would clear rooms when he was tiny.