I think it's worth starting with a few assumptions people make and treat like they're facts. Just because some guy on the internet, or your dad, or even me, your trusted Money Changes Everything writer says something with confidence does not make it a universal fact. Unfortunately, you have to interrogate the platitude, compare it to your actual life, then decide whether it applies to you at all. One person's platitude is another person's bullshit.
It's too bad that your brother and his wife didn't talk about these things beforehand and map out a plan for the future, especially something as important as where they want to live. Obviously, you cannot control what he does, but you might recommend to him that the two of them sit down and review their goals for the future based on available resources, needs and desires.
In a recent survey, 74% of families reported that children have the final say regarding moving into a new house. This indicates the significant influence children have in housing decisions, asserting their views in family discussions about relocation.