I think my dog has cancer?

I think my dog has cancer. He’s a Golden Retriever, and he’s going to be 12 this May. Old, I know. He won’t eat, and when he does, it’s very little. When he was still eating dry dog food he would most of the time vomit it up. Before he would eat and eat to no end. Now, he can’t even finish half a can of dog food. He drinks a lot of water, and since his hips are bothering him, he’s sitting or laying down a lot as well. My parents won’t take him to the vet, saying that since he’s so old that he’s just going to die soon anyway. My mom always talks so blantantly about his imminent death. I nor my sisters want to hear this. I don’t think I could stand to lose him; he’s been there since I was just a little girl. He also coughs a lot, and he’s so skinny, I can feel his ribs when I rub him. Is there anything I could do to make him more comfortable?