I understand the idea and its great if they were able to do that but the world would look a lot different if they would actually do it differently. There would be more houses to buy and they would be cheaper, their money would need to be put in other things to collect interest. The kids would be able to buy the houses themselves at 18 and the parents would have the same outcome, just bad actors would not be able to buy up the market.
To be clear: your extended family is not the problem imo and would not suffer from a law like this.