Mum can have hers back when the pups have been split into single sex cages (i.e. 4 weeks) at the earliest. If mum needs to regain condition then I only allow wheels in the playbox until she has regained the condition. I don't give wheels to my pups until they are 16 weeks old - I've had young hamsters over-run on the wheels, and lost a robo who had run herself to death
You will need more than one wheel per cage if you are keeping them in pairs/groups to minimise the risk of fighting.