I never use the term "fellas" at all, much less to address a gender-mixed group, but my m-i-l always announced dinner that way ("You fellas ready to eat?"), and it was clear that the question was addressed to everyone.

Ny experience is similar. In my case it's my daughter-in-law, who has kept her maiden name after marriage and yet uses "you guys" to be gender-inclusive. ("Emerson!") I have found "you folks" to be an acceptable workaround.