Was your dad an accidental elder or was he reaching out and wanting it?
If he was an accidental elder then it might well be worth your time to have an adult conversation with him (choose your timing damn well) and kindly lay it out that you are concerned for his well being (you are, honestly you are!) that he will burn out and his family is / will suffer, and that you think he is not being fair to his family who should come first. You are though obviously only saying these things because you care deeply about him, (but dont lay it on too thick or he'll know it's not true.)
It has to be framed correctly and delivered without judgement only concern and kindness.
It might make him worse that is a gamble mind, but if he senses you are on his side and looking out for him it might work. If he thinks you are doing it for your benefit he will likely resist.