What a schizophrenic statement. In the first sentence you seem to have your mind made up that this is a cut-and-dry legal case. Then you seem to doubt this position, implying it's not fair to the child, so let's let this couple force a change in the rules at will.
Schizophrenic?
Not any more than "Render unto Caesar the things that are Caesars and render unto God that things that are God's".
Legality deals solely with "the things that are Caesars's".
Legality deals solely with man's law.
Morality deals with the things that are God's.
Something can be legal and moral. Something can be legal and immoral.
Legality and morality have nothing to do with each other. If you are in doubt, have a conversation with a trial lawyer.
As I stated in posts above, it is my belief that the child should be judged by the child's conduct and not the parent's conduct.
That is the issue you should be addressing.
Everything else you mentioned is a non-sequitur.
Fine-- then change the school's conditions of enrollment. Hello???
LOL! I suspect I may be already!