The mother had a claim because the house was literally given to her, which was the right of it's previous owner.
This person has no claim.
If the previous owners wanted it to remain with the family line they should have formalized that by placing the house in a trust.
This is incorrect. The distributor of derivative works in binary form is responsible for providing the source code. They can refer to a server operated by a third party, but if that third party stops providing the source code the distributor remains obligated to ensure that it is still available. The only exception is for binaries which were originally received with a written offer of source code, where the offer can be passed on as-is, but that only applies for "occasional and non-commercial" distribution which wouldn't work here.