It sounds like this couple may be in the position of adopting a child where there is a legal challenge. That's not always something that is known in advance. For instance, a friend of mine has a family member who adopted a child whose biological father was an addict and had never been involved in the child's life (despite frequent invitations) and never paid child support while the child lived with his biological mother. The child was placed in foster care with my friend's family member. After some time, his biological mother agreed to sign for him to be adopted by his foster family, as she understood her own inability to provide care. At this point, the biological father (who had known the child was taken into the foster system and had not offered care then) comes out of the woodwork and decides for the first time in the child's life that he wants his paternal rights.

The bio-dad was a clearly unfit parent, and was petitioning to take his biological son away from the only safe home he had ever known. The child has emotional disorders (thanks to the abusive bio-mom) which the bio-dad was completely unequipped to handle. So, the foster family decided to fight in court for their adoption. Years and thousands of dollars later, they won, but the judge granted an injunction against changing the child's name, so even though the adoption is now final, the little boy has a different surname than the rest of his family.

Sometimes, what should be a straightforward adoption gets really, really thorny and expensive, and at that point dropping it means not following through on a commitment you've made to a human child who now knows you as mom and dad. (Or mom and mom or dad and dad or mom or dad)