How does shared houses work with couples?

One of my married couples just asked to move in with another married couple, including someone in a relationship but not yet married. This would mean if they all move in together, they’d have 5-6 people in the house before having kids. The options I have are to bring everyone they lived with, no one they lived with, choose the other house, or don’t live together. Is there a way to get only 4 of them in the house to leave room for each couple to have at least one kid, or is the only option to not have them live together?