Your constitution and by-laws are the rules that govern your organization, so that's where you need to check. Ours specify that two people living in the same household (i.e., husband/wife) can't both be on the board without special approval of the Executive Board. The reason behind this is simply that it could magnify the possibility/opportunity for funds mismanagement.
I'd have a hard time personally with a clause that just specified "relatives". To me, that's way too general for something like a PTO.
In public office, that's sometimes a concern. And it's a tough one to balance there. I know of a case in a small town where an incoming town council member (very popular, very much wanted) resigned because he was related (2nd cousin) to a lady who had been a secretary with the city for more than 20 years. Had he stayed in office, she would have lost her job! That seemed a bit extreme to me.
Check your bylaws. That's where the answer should be.
several years ago our pto's accountant asked the officers if they were related to earch other. if so, they could not run on the board together. the upcoming pto board may have relatives running for office. how can i find out the legal aspects of this? (we are trying to contact our old accountant, but the elections are coming up soon.)
hope someone can help