Hello Normal: From the sound of it, you are contending with some very difficult circumstances. I would like to suggest that there is a need for you to sit down & take a really hard look at your situation & figure out what your options are. I'm afraid I'd have to agree with your father that if you're living in a trailer that smells like cats, it's probably unlikely parents are going to want to entrust their children to you. This is especially true if, as you say, the market for child caregivers is saturated.
The pain in your back, legs & hips could well be due to a disc in your low back that is impinging on a nerve. If you have the financial where-with-all to do it, I would suggest seeing a doctor about this.
Likewise, if you can, I would suggest that seeing a therapist might be a good idea. This person could perhaps help you to sort out what is & isn't possible for you given your current circumstances. My best wishes to you.