If she is complaining to you instead of him yeah that's bad news she must be really dissatisfied with him. She probably should have divorced before the kid. Shitty situation though wouldn't wanna be her. Pray for her and be there for your grandkid I guess, not much else you can do.
I don't have an answer I'm just agreeing with you which can be useful to better figure out your predicament in that you're not being harsh about the situation.