These are pyrrhura conures, so in the same genus as green cheeks. Basically, whatever holds true in general for pyrrhuras will hold true for these guys. I've never seen one in person. They are beautiful birds. They seem to have the maroon tails and bellies of the green cheeks yet with a beautiful red head. I've been told repeatedly that the green cheeks and black caps are the fiestiest of all of the pyrrhuras, with all the others in general a bit less nippy, but I have no idea if that is true or not. I fell in love with a rosifrons conure at the bird store once, and she WAS sweeter than most green cheeks, but I've also handled many sweet, sweet green cheeks and black caps, so perhaps it is an individual thing. At any rate, you would expect the birds to be at least as sweet as green cheeks.
Considering your grandmother, and what we know of her tolerance for bird sounds, one of those birds sounds ideal for your home.
I am not sure if you wanted something a little larger or not, though.
I didn't find any information as to the adult size on these birds, so I'm assuming it is similar to green cheeks, but it could be larger or smaller. What size are the babies now?