Are you saying he shouldn't have supported his children, and that he shouldn't go see his relatives? That's fucked up.
For most parents a choice between yourself and your children is no choice. He's accepted a level of financial hardship to be, or at least feel like, a good parent. I see no issue with that.
Regardless, you know as well as me - once you walk down that path no one knows it better then yourself.
Context matters. By itself, I would agree with your sentiment. But in the context here, it sounds like you are saying "You should cut your own throat to 'invest' in your kids!" There are a lot of people who really believe things like that. I think it is very unhealthy for them as individuals and for the larger fabric of society.
You're right; but I am a child, and there's no way I would let my parents help me buy a house if it meant that they couldn't retire comfortably.
If you were his child all you'd probably have seen was that he sold his house and offered to help you get on the property ladder with some of the money he released. If that happens and you believe that he's got other savings then that's a very different situation to be presented with than the idea that you're messing up his retirement.
But even if that weren't the case it would surely be a failing on their part rather than on his?