1. Disabled people should not reproduce with each other if it is very likely that a deaf child would result from their union. You know that if they hadn't been homosexual, they would've each found some deaf spouse & had deaf children for themselves.
OR
2. The right to choose one's own egg/sperm donor. At my college I saw an advertisement for an egg donor who was a honor student & at least 5'10", so I'm assuming that there's no law against choosing a donor based on specific trait.
What they did was sick, just saying that I don't really see a legal basis involved unless they actually physically hurt the child to induce deafness... #1 would open up too many cans of worms.