One bedroom per child has become the rule in real estate. I am not sure why as when I was young a lot of my friends used bunk beds. Very common.
The happiest day of my life was when I got my own bedroom, and I didn’t have to share it with my brother anymore.
In ultra-Orthodox Jewish homes, bunks are VERY common. Hassidic Jews, especially, have very high birthrates; ten children is not unusual. In fact, they would wonder about you if you "only" have four.
In Judaism children are considered a blessing. Also, the community helps its own -- huge number of charities & services.
To be sure, some do use birth control, mainly to space children apart. But ultra-Orthodox Jews have religious incentive to reproduce -- and there lies the rub. Without a culture of marriage and children, and culture of mutual aid, singlehood will be the norm.