Yes, it is.
It, in my opinion, would be best to have separate rooms. Or the alternative is to have separate beds.
In most states a 11 year old and a five year old can share a room, even if they are not the same sex. However, the 11 year old may not enjoy having to share a room with a 5 year old.
No, step parents do not have any legal rights to the kids.
A 13 year old girl and an 18 year old girl can share a room. Sometimes, girls must share a room out of necessity. If this causes problems, then each girl should proclaim a side and keep their belongings there.
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yes they can
It is not illegal for siblings to share a room. Age has nothing to do with it.
There are no laws saying parents and their children cannot share rooms. Parents and children routinely shared a common room in most poor households until a generation or two ago, even if it is less common today.
No.
Of course. I don't think he'll be happy about it, but there is no law against it.
Not until you are 18.
No, she is too old to share a room with a 5 year old. As a preteen she is starting to develop and learn about herself in relationships to the world and other people. Life is confusing enough for a girl her age without having any privacy. A 5 years old doesn't understand giving another person space and is very egocentric. The teen is also egocentric and very concerned with looks, hair, clothes, and what others think. Together they will not be able to share a room for very long without problems.