We have an blended family and I would like to know what the LEGAL age that I should split rooms. The children are Boy:5 Girl: 4

Welcome to the wonderful shady area of the law. There is no real "law" that I have ever seen or hear of.

What happens is there is no problem unless a step parent files a complaint in family court or unless there is reason for family and children services to investigate you. Then they have rules.

So while this is no help, part of the issue will be is the other parents of the children in the blended family having problems, filing complaints and so on.