Thing is if it was time to take away from the mother then all you'd have to do is put them in separate hutches, girls & boys. I do believe that the humping in your case is not for reproducing but just what rabbits do. My spayed females, one of them starts humping and it sets the others off. Obviously nothing is going to happen as they are unable to have kits but they still do it for some reason (not constantly now they've been spayed).
My suggestion would be to wait until you feel all the kits are eating and drinking on thier own and are ready to leave mum and then separate them by gender. I'm sorry if this isn't much help but it's all i can give.