You are right to support your daughter in law and the children, and I think, at present, stand back from your son. No need to estrange yourself from him, but at 44 years old he has to take responsibility for his actions, and managing his illness without your support.
I have a friend whose son has behaved in a similar fashion, leaving two wives, one on New Year's Eve, three weeks after their wedding. Fortunately no children, of his own, but his mother can see no wrong in him, and always blames the wives, and previous and present girlfriends, of whom there are many, for the inevitable discord.
You can see your son clearly, and I think you are absolutely right to consider yourself as well as his abandoned family, before his needs.