I was driving earlier and I've been noticing my brake pedal kinda vibrates a little bit, and my back brakes or differential or something is making a squeaking sound, and I looked back there and there's fluid dripping down on the inside of the rim, what could be the problem?

 

That's a good indication of a leaking wheel cylinder. The squeaking might be loose shoes moving excessively. I'd pull the drum and if a wheel cylinder is leaking, replace it. Clean everything up good and readjust the shoes. The squeak may be gone afterward.

 

If you replace one, replace them both, do the back brakes as well, and be sure to clean the drums out thoroughly. Either that, or just replace them too.

 

Like said, wheel cylinder is blown. And brake lining might have worn out which causes the squeking.