Very sad. They are both locked into this situation which they have mutually allowed to continue for 25+ years. They are both getting benefit out of it even though they are both frustrated as well.
I don't think there's anything that can be done at this point, frankly. If she couldn't kick him out when he was 20 or 30 or 40, what's different now? She's more dependent on him now than she was then as she is so much older. If she didn't teach him the skills he needed way back when, just demanding that he leave is going to take too much out of her at this point.
He may feel that the house will eventually be his. Or, if there are other siblings who co-inherit, they will have to decide about selling the house out from under him (at which point he will have to find subsidized housing for someone who is emotionally disabled or whatever his problem is), or allowing him to continue living there as he always has (for as long as he can pay the upkeep and taxes).
I honestly think it's a little late for family counseling and all that. They are so set in their ways and, on some level, this situation has benefited them both for 48 years. I don't think there's some miracle that will make him get a job.