My Dog's are sick and I don't know what to do!!!?

I have two dogs. A cocker spaniel that we rescued from mistreatment, and a over-sized Boston Terrier we rescued from starvation. The Cocker Spaniel's name is Tess and we don't know how old she is, but we guess around 8 or 9, maybe older. Her back leg has been limiting her mobility, and she won't eat dry food unless I let it sit there. She's also been whining a lot recently. Tonight Tess started scratching my door and whining almost to a bark, so I opened the door, and she had me follow her. She led me to the bathroom where I found my Boston Terrier, Brianna, eating her own runny crap. Brianna has been estimated as being two when we got her a year ago, but she has grey fur around her mouth and in her ears. She is very large though we were told she was pure bred. She can't smell that well at all, and she's almost blind judging from the cataracts on her eyes. I put both dogs and out, and gave them fresh food and water. Brianna ate a little, and Tess refused to eat. I found multiple piles of crap throughout the house when I got home today, and Brianna chewed through my mom's shades. We can't afford a vet. What is wrong with my pet's? What should I do?