Daughter-in-law refuses to pay widower father-in-law $400 a week to live at his mortgage-free house so she can take care of him: 'My father-in-law inherited roughly $300K. My husband and I received nothing.'

She's not going to pay to be a caretaker. 

There's a huge discrepancy between moving into your in-laws' home because you're down and out, and moving in because they're down and out. Many young, newly married couples rely on their parents because they don't have enough income to support themselves. Maybe one of them is going to school, and their single income means they have to live at home for a year or two to save up for a house. In that circumstance, the young couple might be indebted to their in-laws. They might be expected to pay them rent, and that's their in-laws' right!

It's totally different for a young family member to move in with their aging parents to take care of them. 99% of the time, young people do this because they and their parents are not in a financial position to hire a healthcare worker to come into their house and assist their parents as much as they need. This arrangement can breed resentment because it stymies the young family member's career. Few people can work full-time at a job that makes money, and take care of their elderly family members full-time, making zero. In these scenarios, it's common for the young family member to support their parents if their parents don't have a dollar to their name. Otherwise, it'd be kind of inappropriate to ask your kids to pay you to work for you.