I think in typical Yuri stuff that tries to involve kids, it's along the lines of adoption (less legal form, more just taking in a kid and treating it like a family), pseudo child (think some kind of cutesy spirit created from both their mana or lab experiment in the rough shape of a kid or something) and it's at the most extreme end we get magic/science babies (mcguffin to allow an actual pregnancy with both women as a parent). You gotta understand that in a lot of Yuri works, even the presence of a man in any shape isn't really depicted beyond background fodder.