There are many times when tragedy occurs in the life of a family, and they need every member to help them through it. For those who have in-law issues, it can be a time when they prove to the family their worthiness to be a part of it. Looking at an issue as an outsider can be a good way to help bring calm to the situation, and it might even be part of the solution.
A family crisis is an emotional time for people who have been together for decades, and resolving the situation could be difficult for those involved. A person who is part of the family without being accepted might be able to spot a clear path to resolution, and they could have their spouse present it for them. After all is said and done, they family might still be hesitant to accept that the spouse provided their solution, but it could also be the start of acceptance.