If they don’t want to have rules that our society finds acceptable they don’t have any right to just exist. This isn’t a person were talking about they are an education institution. A school cannot by definition have a religion because it isn’t a person. I don’t particularly care if the people wo made the school are themselves religious; that should not give them the right to use their new founded institution to enforce those beliefs on other people. If you want to teach people I think you should be held to certain standards, and one of those standards is that you shouldn’t restrict the freedom of your students.
Having sexual morality rules is absolutely restricting their freedom. People have a right to privacy that such rules inherently violate.