How many musicians? Four plus a cellist
Playing what instruments? Guitars, bass and voice
Arranged how? Unplugged
In what physical space (dimensions)? Dunno really, but it's a pub and I expect it to be quite small...
Any idea of the room acoustics? Nopes
What sort of overall environment (you mentioned bar, but do you anticipate a chatty, quiet, or obnoxiously drunk and loud crowd, etc.)? I guess we'll ask the crowd to stay a quiet for respect to the musicians.
Sorry, I wasn't clear - I meant arranged how with respect to one another, and whether seated or standing. Like in a half-circle, or straight line left to right, or two in front and three in back (or vice versa), etc.
If they're in a a straight line left to right, XY will work nicely, I think. It's already a very wide soundstage due to the musicians' layout, so XY will capture the soundstage well without exaggerrating it.
If they're in a half-circle, DIN or ORTF might work nicely just outside the half-circle.
If they're in a corner kinda two in front, three in back, maybe back off just a bit distance-wise, else the front row musicians might overpower the back row musicians. Moving back will allow for some blending of the instruments/voice so the front row doesn't completely dominate the sound.
If you're able to do any sort of stage setup / practice (I'm guessing not), then walk around to determine which spot sounds best. If you're running cards, as you walk around, place your hands facing forward, flat behind your ears, and cup your ears forward just a bit to simulate the more directional pickup of the mics.