“Who” is the correct word because it’s the subject of the verb, not the object. The subject being in a parenthetical phrase has nothing to do with the pronoun.
The parenthetical phrase means that the phrase is to be considered separate from the sentence. That’s important for some to note because it helps some folks see how to set up the sentence (and isolate the phrase) and not try to connect said phrase artificially with the sentence into which it has been inserted.