Is there a fancy name for these letters that "hang low"?
Yes, they're called descenders, a term which also refers to the part of the letter that dips below the line.
They have descenders. I don't think the letters themselves have a name.
Edit: I stand corrected.
a. The part of the lowercase letters, such as g, p, and q, that extends below the other lowercase letters.
b. A letter with such a part.