Kids in legal gray area when gay couples split
By Richard Willing, USA TODAY
Two women in El Dorado County, Calif., Elisa Maria B. and her domestic partner Emily B., decided they wanted a family. So when Emily became pregnant by means of a sperm donor and gave birth to twins in 1998, the lesbian couple faced a lifestyle choice. Emily, the couple decided, would stay home with the kids, one of whom had Down syndrome and required constant care. Elisa would be the breadwinner.
Ref. https://www.usatoday.com/news/nation/2005-06-20-custody_x.htm
To me this is cut and dried. The birth mother has first 'dibs' on the kid. I think that if the partner has been around since the beginning and has been a parent, then joint custody should be applied here. But the mother usually has primary custody in divorce cases, so it should apply here unless a good reason to do so other wise is shown.