Can you invite friends to the UC bar if there in PE or B+S.
I have done on many occasions, but it's up to the IFS - they will normally agree if it's not too busy, and your guests are only popping up for a limited amount of time. Obviously anything which would deny an Upper Class passenger a space at the bar is avoided.
Best to ask the IFS shortly after take off, and be as understanding as possible (so they know, you know the situation)
Pix