Allowing the lesbian couple to marry would have eliminated most of the legal problems you're talking about. Rather than walking away from her obligations to her former partner a divorce action would have been required. Property would have been divided. Parental rights and obligations defined and ajudicated by a court. The deadbeat mom would be forced to provide for the child she agreed to care for when the decision to have a child was made.

The poor gay man that helped out his friends has learned one of the axioms of life: No good deed shall go unpunished. He should have made a contract defining what his rights and responsibilities were before making his donation.