It sounds like a conflict all right! My first concern would be that their personal issues would get in the way of the board functioning properly.
Voting to benefit your own child is an issue for all board members, so that's less of a concern for me. A group could have two board members with children in the same classroom who might also vote the same way, for instance. But the bottom line is it's OK for the battling exes to both serve unless your bylaws specifically prohibit it.
- Craig
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