Family member neglects dog

[Catlover94]

Hello there, I'm seeking advice on what to do. My aunt and uncle have a dog she's about 13 years old now but since my aunt and uncle have been together (7-8 years) they have not once taken her to the vet... it was my aunts dog so who knows how long before that. Often I find her nails are growing into her foot pads, she's been limping for a long time now, she's becoming increasingly aggressive, her teeth have been rotting out of her mouth for years now. A few of them are completely pointing straight out of her mouth, her breath is horrid and she chokes a lot. They seem to think the dog is fine but I cannot stand to see this dog suffer like this. It isn't fair and I can't sit by and do nothing anymore. They can afford all this frivolous stuff but when it comes to vet care "they can't afford it". I am thinking about calling the SPCA, although it will be hard because they are my family but I think they should have to face consequences for being so selfish. Any advice?