IF real musicians are involved who know how to play a small room, and IF the 2 drummers know how to play with (and not on top of) conga, bongo and djembe players (and vice versa), the only reason for a PA is for the vox and harmonica. A very small PA, maybe even just 1 good speaker on a stick, would be adequate. This would be an easy and fun gig, could be great. IF these are not real musicians and don't know how to play a small room, bring your earplugs and charge a lot or don't do the gig. More fun to stay home and check the solder connections and continuity on all your cables. Seems that the big IFs are key here. We do lots of small bar gigs and have a great time, until the DJs blast music between sets and chase all the musicians out.