So this has been driving me nuts because I can't quite seem to figure it out, and it's language related... though English, so maybe I can get some help here. I'm just trying to figure out the part of speech for the word "all" in this sentence:

They are all jealous of me.

I think it's an adjective, but can you have two adjectives in row in a sentence like this? I thought it might've been an adverb too but "all" is not describing jealous, it's describing "are"...