I am not sure if I will say anything at all... maybe I will just let the lease finish and then withhold some of the security deposit (can I normally do that in this situation, claiming that the illegal 6th tenant increased wear and tear?).

I found this article on Florida law by the bar association, and it says that before a tenant can withhold rent for a place being uninhabitable, they have to first give the landlord 7 days written notice so the landlord has time to fix it. 

In both cases, sending a letter saying that if it wasn't resolved in X amout of time, legal action would be taken, solved the problem.It probalby didn't hurt that I wrote a CC on the bottom letter to a family member that is an attorney.Many states/cities have special regulations stipulating that landlords improperly withholding deposits are libable for multiple times the money withheld. 

So, they look up the laws that say they can get out of the lease if the place is uninhabitable, or they can withhold rent if the landlord doesn't take care of a problem, etc.  

Unlawfully withholding a security deposit will result in having to return 3 the deposit if you go to court in this state, not sure about where your friend is.

If you withhold part of the rent, he is going to file for eviction.

Therefore, I've opted for 3 months with hold over reverting to m/m.

If the repairs effect the safety or habitability of the unit there are further steps such as withholding rent that should be considered after a reasonable time to repair is given.

Change your withholding on your W-2 and save the extra take-home pay.  

So far she has not mentioned this to me either by text , phone or any letter2) There have been no written demands of repairs or anything notifying me that tenants will withhold rent so I do have the option to take her to court for eviction.