We have good size bedrooms and enough bedrooms so each child can have their own room but we double them up so early on they learn about sharing and respecting someone else’s things. There have certainly been squabbles but they are very good friends. I remember once telling them that if Dad and I can share a bed you can share a room.

Upper elementary share a room with a bunk bed. Older one is generally happy but sometimes needs his own space so let him sleep on a mattress in the den. If you have a basement/attic/den, oldest could transition there at some point. If not, they will be fine.

There's nothing to it. They know to be quiet when the other is sleeping. They've known this since the youngest was 3. They each have their own drawers and shelves, and share hair accessories and books, and one shelf is mutual games/dolls.

It's been working out fine for over a dozen years.

I have 4 kids (tweens/teens) in a 3 bedroom. The boys share and the girls share. I am not sure what you want to know about making it work. Bunk beds until they get older. Now my teen/tween girls are asking to get out of the bunks. We live in a small house in the city. No shot of moving -- though we never really considered it. I grew up in a large family and had my own room for the first time my senior year in college. Teaches kids lots of life lessons.