I see it as a case of two parents on one side and a sperm donor on the other side. I don't think the genders or sexuality of those involved matters one iota. This should be dealth with in the exact same way as if it were a male/female couple and a heterosexual male donor. The women raised the children, so they are the parents. If they want to have the donor/biological father involved, then it is up to them to decide the extent of that involvement taking into account the children's ages and also their best interest.