Is it a good idea to tell my estranged brother that he has to go to a psychiatrist if he wants to be back in my life ?
I'm interested in your brother's life story.
You should be. It's painful to see my own brother going through rough times.
It sounds like your brother has a lot of problems, in that case it is okay to give him an ultimatum. If you let him back in your life too easily you might regret it.
Nah, My brother is in no position to hurt me considering  his mental situation.
Then probably you did the right thing by asking him to get some help. You should help him in any way possible.