So we had solved it back then: When the children were very small, they slept on the same floor. Shortly thereafter, we "released" our bedroom on the ground floor, which freed up a larger children's room; the kids were happy, still within earshot for us. We moved to the basement and set up a large bedroom with a dressing area there, all in lightweight wooden construction (DU/WC also available in the basement). As the children grew older, it went the other way around again, and when they left the house, the downstairs became a guest/office room. We never hesitated to adapt the rooms to the changing circumstances. Back then, we should have insisted during construction and kept the option open to create two separate "apartments" in the basement with, for example, a shared DU/WC in between. Children, grandma; illness, separation... who knows... Ultimately, you won't be able to accommodate everything under one roof now. I would, as far as possible, keep the options for later remodeling as open as possible, because although you want to anticipate many scenarios now, in the end you don't know which others will actually occur, usually the ones you didn't expect. In addition, children's development can be completely different; therefore, flexibility was key for us, which I would always do again. However, you must not be afraid to occasionally replace a wooden wall or retroactively build a door into a wall. For us, it was always worth it.