The adoption story does raise a question that some parents may justifiably wish to leave until a child gets older. Most children don’t think about who’s married to who, until something is raised that is outside of their zone of assumptions.
Would the other commenters here be ok with a story of Jack and his wives Jane and jean? If everyone in jack’s family is ok with it – shouldn’t it be ok to have in a book? And before someone says “that’s not legal” remember that gay marriage isn’t legal everywhere. Note: I’m not in favor of polygamy- just making a point.