Oil dripping from rear of car that smells like burning rubber and is green.

Ok. I needed the dashboard speakers replaced on my 1999 Jeep Grand Cherokee. When I went in, they said my brake pads were 3%. THe mechanic quoted me for oil change, speakers and brake pads $2,700. Didn't have enough so just left. Next week I was in a car accident as passenger in a Nissan Xterra and hit head on by drunk driver in pick up.
Car rolled off cliff after flipping 3x. Thankfully I can't remember any of it except waking up 2 weeks later with 3 fractured vertebrae. Unfortunately, because of my injuries I was fired from my job. I am a widow with a 10 year old. Because we couldn't remember anything, insurance went with drunk's (he was arrested for drunk driving) statement that he didn't do anything wrong. He had no insurance (of course!)
The car started squealing when I hit the brakes. Then vibrating when slowing off highway. I postponed doing anything that would take money, hoping for a settlement or a new job. We had very little in the bank and now nothing and I am still scared. But my friend's nephew is a mechanic and will do all the work for free next week. Great! But now it vibrates all the time and there is oil dripping from near the rear wheels and center round thing in rear(differential?) Only after driving. Not when still.
What is broken? What needs to be done?
I feel bad and I know it would be cheaper right away. Just scared on how we will cope with rent, PG&E and food needing to be paid for still.

Please advise.
Sorry for rambling on, just a lot on my mind.