@tupp were you able to modify the APN settings after all? I ran into the same confusing situation in the API settings on the phone.
Thanks. looks like it might be on the carrier end. I spent a good bit of time messing with the carrier settings, but could not get group MMS to work.
Do you have the link for that item on github?
Can't get MMS groups here either. Using Nexus 5. I can send out a group text, but the recipient sees the text only from me and I receive responses as if it were one on one.