Hammerman, I don't know what to say. I'm at the other end of the spectrum with a baby (5 months yesterday) who sleeps for England and has done since he was born. I do sympathise with your daughter.
During his waking hours he gets lots of stimulation but I don't have to hold him constantly. He has a little playmat (sensory gym mat, or whatever it's called). He likes watching Tiny Pops. He loves routine.
OH and I certainly take our turns to feed him and see to him and we have a fantastic support network in OH's parents who have endless patience. If your daughter is having to do the bulk of the parenting herself, I can understand how she's struggling - I certainly would, and that's with a very good, contented baby.
I just don't know what to say because, despite him having his moments, he is on the whole a very good, easy baby. I can only imagine your grandson will grow out of it.