okay bear with me through this explanation...

I have 3 boys 5, 3, and 8 months & due in November with a girl. We have three bedrooms upstairs and two room downstairs one is being used as a gym the other a guest room. The youngest babies will be in the nursery together which is located across the hall from our room. My oldest boys currently share a room. My husband and I are next to them in the master bedroom. My questions are....

1) How long is it ok for siblings of opposite gender able to share a room?

2) Is it okay to move my oldest downstairs in a few years by himself ?

what would you do?