One is Kitten is apparently Male

[Beckie85]

we got kittens at 8wks old thought we had 2 girls. Turns out today we found out one of them is male. They are 7 months old. We hoping to get them netured as soon as possible. Panicking about pregnancy and hoping cause hey have been together so long they won’t stop getting along. Any advice or reassurance would be greatly appreciate.

Had they never seen a vet before now? They would have picked up that they were different sexes. Hopefully the female isn't pregnant already

Ours were sold to us as 2 girls and turned out to both be boys. Picked up at their first vet appointment

Sex doesn’t make much difference to compatibility. They will be fine but your female one could already be pregnant do get a wriggle on! The male won’t care about his sister!