fighting and aggression are pretty much a given once they start to hit puberty. generally here in the states they neuter boys as young as 3 1/2 months, but often they encourage waiting until 4 months for girls. Some vets prefer to wait until 5 months for both, since buns can reach sexual maturity at different ages.

Since buns can get pregnant as young as 3 months old, I would recommend not housing them together for much longer And since Flo is still unspayed, she certainly could wind up pregnant by one of her own sons.

I’ve had a lot of good luck with brother or sister pairs, at one of the rescues we had 5 bunny girls that lived in a little herd and got along quite well. The only problem is, that when you start to get the bunnies spayed and neutered, when you have to take one out to go to the vet, and then keep him/her separated while he/she recovers, its going to be tough to re-introduce the bunny BACK to the pack. I think that will be one of the biggest problems. I’d recommend separating out brothers and sisters, or going to get them spayed and neutered in pairs. Do Flo and Dad ever just lay next to each other or groom each other? He may be trying to establish that Flo is “his” since the boy babies are getting older.

Our boy DJ still chases his friend Curly Sue, even though he was neutered many months ago.  This behavior is particularly apparent when we have foster bennies in the house.  I think it is a way for him to show other bunnies that Curly Sue is "his".  i think as long as she does not fight back, you are OK.

When Juli and Kramer encounter foster bunnies it usually turns into a big “spat” and someone loses some fur (or in most cases, they BOTH lose some fur) so I think, as Osprey said, that Thunder is just feeling a tad insecure with all these young buns running around (I don’t think that buns have much of a concept of the word “incest!”)