Unsure, but I do recommend going to a rabbit-experienced vet (exotic vet) and having them all assessed. If they are younger than 8 weeks, it is very unhealthy for them to be away from their mother’s nutrients and this can lead to poor development, so a rabbit vet will be able to educate and inform you on actions to take in order to facilitate healthy growth.

My Wick is a netherland dwarf, and he is a runt, meaning he was the smallest of all his siblings (half the size). At 9 weeks old, he was slightly larger than my hands, so for a cross breed, neither of which are known to be small, I really suspect they’re younger than advertised, or are a different breed.

Are they your first rabbits, and are you aware of bonding processes if you plan to keep them all?

That does sound small for an 8 – 10 week old larger breed rabbit. If they are 10 weeks of age, they will soon be entering puberty, which means that you will need to separate them in a couple of weeks. Even if they are litter mates and have been together since birth, once their hormones come into play, everything changes and they cannot stay together. You risk fighting and severe injuries, and you risk pregnancies. It can be difficult to sex rabbits, which is why some people end up with surprise litters.

I agree with the above. At 8 weeks my two Holland Lops could not fit in the palm of my hand, maybe 2.5 palms, but not one. I think a vet visit is definitely in order just to give them a good once over. Also I echo everything Toby said about keeping them separate at all times, not even supervised play time. When they get older you can read more about bonding on the bonding forum.