Welcome here!
First question, they are all spayed and neutered, right? Just have to make sure because if they’re not, we can be getting into some serious issues. Also, pregnancy aside, it’s not enough to just neuter the male, the females have to be spayed because of the high risk of uterine cancer.
I would move them into the new living space now and work on littertraining there. Tanks are not good for housing rabbits because of the reduced ventilation. Also, even if they pick up on the litterbox in the tank, when you move them, you would have to start all over.
As far as the dog crate, how big is it? Each rabbit needs to have a minimum of 2×4 feet, so any space they are confined in would need to be some variation of 4×6 feet or larger. If you’re doing multiple levels, you have some leeway on that, but you’d still want the base level to be 4×4 feet. In too small, or too large, of a space, littertraining is very difficult. There’s a fine line that will work for groups.
That being said, it’s impressive they are all getting along as such a young age.