Fights and drama at my property

[Jeremy Mangen]

I'm just curious what other landlords have done to handle this odd scenario.

I'm a new landlord and I just got my first duplex completely rented out. I was told last night that there was shouting and doors slamming and all that drama stuff happening in the common area in front of her unit (its an up/down duplex and they were fighting at the front entrance in front of the first floor units door). 

I asked for more information and then sent an email to the other tenant asking her if something was wrong or if there's anything I can help her with to prevent this from happening again, but how would you handle this? Especially if it happens again. 

I will be installing a security system but if a tenant lets someone in I can't stop that, but there are a lot of kids living in my duplex and I'm 100% vehemently not ok with fights happening in a family friendly building.

Thanks guys!