If they want to talk about their son, I dearly hope it helps them deal with their loss. I don't know anyone who doesn't feel for them, as we do for anyone else who has lost a child.
If they want to talk about how they know what being a carer is like for most ordinary people - they really, really don't. They haven't had to spend years of never having enough sleep, of debt, of shortchanging other children in the family of time and attention because there aren't enough care-hours to go around, to not knowing what is going to be your fate in the next week, month, year, decade...
It's that feeling of hot, bright exhaustion washing over your brain when you are chronically sleep-deprived over months and years, you have to take three buses between appointments because you can't afford a cab, you can't stop, you dare not get ill yourself, your paid work hangs by a thread as you can't focus on it and you have to drop it every time there's an emergency, your home is a state because you don't have time to do housework, you eat cheap rubbish because it is easy and cheap and it gives you just enough energy to get stuff done, there isn't anyone to hand any of this over to, you feel like you aren't doing enough for any of the people you have responsibility for but you are doing your best, and you have no idea how long it will go on for....
It can be utter desperation, being a carer, and while they have no doubt suffered great pain and loss, they haven't known this.
YANBU.