Stereo vs Mono

You have two distinct sitting area served by each pair, thus, I would stick with stereo. Why not? And where you have ‘overlap’, reverse. In other words, reverse the R&L as you are looking at them, as one pair are on the ‘inside’, the other pair on the ‘outside’. I would probably keep the R&L ‘correct’ in the sitting area, and let the dining are be reversed.

Really, it’s more for casual listening, right? So I don’t think I would care about perfect imaging and soundstage as in a critical listening room.

Mono, without a fixed seating location, stereo is going to be non-existent. 

Stereo effect depends where you sit. It will sound like mino or better. Mono will sound llike mono or mono.