I have the cutest images, I don't think I would move them into the cube until they are the same size as the chooks in there. This is based only on what I have read though I have only had chickens for 1.5 weeks.
My broody is in a separate house & run to the cock & other laying hens but they frequently all meet whilst out free-ranging. The broody is not standing for any nonsense from the cockerel and fluffs herself out quite menacingly. But her chicks are only 3 weeks old.
At 7 weeks, your chicks are about to get dumped by mummy, so will have to fend for themselves. I'd see how they get along and move them elsewhere if necessary. The ladder shouldn't be a problem at all, though they may fly at it!
Keep a sharp eye on the newest hatches as they may get trodden on/fall in the water/fall down the ladder and get stuck etc (all of which happened to mine!).