Life is all about choices. They can choose not to live in the same area, to downsize, not to send their kids to an expensive college, let their kids pay for college through loans, they can take out loans, etc.

Why should I subsidize their choice when I chose to live in an area where the cost of living vs salary is much more amenable to my choices and financial goals for me and my family?

Yes, this means they have saved 1 million dollars vs buying the house today which would cost them the full amount.

...which they'll be able to afford, since they sold their house for 1.2MM.