Good news. I think you learned a good lesson (we all do, in different ways). Tenants teach us.
With shots fired and weapons brandished, you definitely got one end of the spectrum (the bad end). It may never be worse in my opinion (can't get much worse than that)..
The tough part about landlording is that you end up absorbing some of the fallout from the deficits and issues in the tenants' personal management skills.
Be it issues with rent, interpersonal relationships, communication, even violence or drugs and alcohol, their problems become yours for better or worse.
For me, with bricks flying, sirens wailing, guns firing in the first couple of weeks--I get out my check book and wish the wheelchair fellow all the best. Then I see if I can do the same with the other tenant.
I think I would also say it is "not a fit" or working out and lay out a reasonable cash for keys arrangement (and maybe mention the alternative would be a for cause eviction on the bricks, sticks, and bullets)...
I would just call it tuition at bad tenant university.
That said, if you are going to willingly be in this gritty type tenant group that resolves disagreements with gun play, dodging bullets and such, then I would maybe up my life insurance, get a bullet proof vest (really, I would for late night visits about noise calls) and rent to the remaining tenant and hang tight for her next adventure or interesting co-habitant as you will have a front row seat for all the action.
Best of luck!