How to help my family take better care of their dog?

I live out of state but come home to my parent's house at the holidays and sometimes for a few days in the summer. We got a poodle puppy in 2001 when I was a kid and now, 12 years later, my family doesn't pay any attention to him. I come home for Thanksgiving and he is smelly and ungroomed, with mats in his fur, long toenails, and hotspots where he's been scratching at himself. He's stubborn and has to be coaxed out of his crate to go potty using cheese and other treats. Sometimes he will stay in there all day because my parents go to work in the morning and don't have time to spend 20 minutes trying to get him to go outside. If he does want to go out or be let back in he will whine until someone opens up the crate/opens the door. He can be aggressive around food or if anyone tries to put him on a leash/disturb him from his location on the couch. He will jump on people asking to be petted. At the same time he can be very affectionate and sweet, and loves going on walks once he is outside (although it is impossible to get him to heel). My parents protest that he is "untrainable," that they've tried working with trainers, and have basically thrown their hands up. A lack of money for training and pet care is not the issue here. They make sure he has food and water, and take him to the vet when they need to, but they're so frustrated that they've given up doing anything else.

It doesn't help that we have two adorable, well-behaved, low-maintenance cats, so our poor old family dog languishes in his crate all day long while my parents and youngest sister ooh and ahh over the antics of the kitten and older cat playing together. The dog and youngest cat snap at each other sometimes but my family just laughs it off and thinks it's hilarious. I'm not there very often and couldn't take the dog back home with me, but I don't know what I can do to convince my parents that our dog deserves better treatment than this and that his bad behavior is affecting their quality of life as well.

Any suggestions?