A different perspective:

Both my family and my husband’s are middle class.

It doesn’t matter. My parents still didn’t think he was good enough for me. My mom didn’t like his lack of religion, said his parents were “hillbillies”, hated that he didn’t have a college degree. My dad was pissed he wasn’t some well-earning executive or famous athlete.

Basically no one was good enough for their little princess. But three years and two kids into this marriage and they’ve done 360s. They love him like their own son.

Why? He’s taken care of me through major illness, stood with me through childbirth and helped care for sickly preemies, changed careers and works 13 hour days so I can be a stay-at-home-mom...he’s shown them that he’s worthy

I don’t know if these people have it in them to accept you, but I thought I’d offer this up. Have these people ever liked one of your GF’s partners? Is there something you could do to show them you’re serious about your GF?