Depending on where they live.... and since they seem pretty home-bound due to their health,
why don't you, Hubby, and your children... go to THEIR place,
cook dinner, make dessert, and maybe the kids can put on a little "song/dance" routine for them?
THEN, get a tape recorder, and let them talk about their life.... do an audio "diary" of them... it will be a nice interlude for them, lets them share their life, and you/Hubby/your children will have something "recorded" for a souvenir for when they are no longer in the human world. I have found, that often times, elderly LOVE to talk about "themselves" and their lives... because often by this time, and at this age and with health problems... people don't often "listen" to them anymore... and they miss that.
Or, have a family portrait done, with them in it too?
Me, I adore the elderly & especially since after my own Dad passed away... and somehow I always bump into elderly who will just talk and talk to me, even though they are strangers and I don't know them. But I can see in their eyes that it gives them such "joy" to have someone actually LISTEN to them AND ask questions and be sincerely interested in what they have to say and share.
Perhaps, your parents would also enjoy this... real "quality" time... and sharing it together?
Just an idea,
All the best,
Susan