I'll go with 4. I think she is bigger because things have already been stretched out.
this is the 2 we kept from her last litter they were only 7 weeks old in these photos i will have to capture them again so i can show you how huge they are now
Guess your son will get to choose which one to keep.
i think we might just have to lol we also have 2 a pure black girl and a tuxedo boy from her last litter which we kept its just one of those things being able to have a kitten from birth but these will both be neutered when Missy goes in 6 weeks they should be old enough then