My father is in rehab and is scheduled to leave, but the rehab center is putting restrictions on the family to release him. Is that legal?

Here is a link to an ombudsmen that can be the mediator for your issue. Good luck.

http://www.aoa.acl.gov/AoA_Programs/Elder_Rights/Ombudsman/index.aspx

I'd talk to the doctor and see if he is really ready to leave. You'd have to check your state laws to see if what they are doing is legal, but I'd think the doctor would be your greatest resource.
Good luck,
Carol