Ariel, Amelia, Domonic, and Brian used to answer a lot of fan questions. Sabrina did some but I think she toned it down a bit since one fan accused her of not drawing enough POC characters. I dunno about the rest but those are the ones I'm aware of that I follow.
Nefcy doesn't do Tumblr questions, but she'll retweet and tweet at fans. Same with Adam.