ah word, that makes sense.
I agree that it looks like the BB could be on something marginal. So many people yet to act and he just flats, it's got to be like TT or a similar ace. I really don't know what the standard of play at 25nl is like anymore, so I don't know if your 'average' unknown will lay down a hand like that to a 4bet. Another issue is the bet sizes. We've got 25 effective and utg has just put in >1/5th of our stack, so a raise is definitely going to commit us.
To me it looks like it's either fold, or shove. I'm leaning towards shoving to scare out the BB and get the fish isolated.