Wiktionary
co-parent
n. someone who shares in the parenting of a child or children, such as: vb. to act as a co-parent, to share custody of a child or children, to share in the responsibility of parenting a child or children
Usage examples of "co-parent".
Since space is mainly empty and near stellar collisions most rare, it was concluded that few other planetary systems exist—perhaps only one, around that other star that long ago co-parented the worlds of our solar system.