No overnight visitors.

If the inspector did not see signs of pests or recommend that an exterminator evaluate the situation, they may be new visitors.  

Pretty much any city/county in the United States has what is called an Transient Occupancy Tax (TOT) which is levied on visitors to a given area and normally collected via Hotels, B&Bs, etc.  

One is being sued. 2 were forced to declare bankruptcy and the one being sued is going to have to most likely.They all got over leveraged, didn't have enough cash to make the places nice, no real reserves and then the pandemic came along with the various municipalities restricting visitors etc.

My biggest concern is if my tenant's visitor found the firearm and used it on the premises even though the tenant him/herself worked for law enforcement I want to make sure i'm not liable.

Every time you think about, talk about or actually visit or work on your property, just imagine taking a $100 bill and throwing it away.Not to mention my favorite saying - "Money is a renewable resource, time is not"....

Then mark the other two as visitor and limit it to 4 hours (or whatever you think is reasonable). 

Vehicles may not be parked on the grass.Tenant agrees to advise their guests/visitors about parking and agrees to be responsible for improperly parked vehicles of their guests/visitors.Assigned or unassigned parking spaces (or carport, if any) available for use by Tenant are intended for the parking of private passenger vehicles.

If you add your roommate to your policy and a visitor is injured by your roommate's dog, the liability policy would cover any damages.However, adding your landlord as an additional insured makes it impossible for either of you to make a claim against one another's liability policies for damages.For example, if faulty wiring causes a fire in your apartment, you and your insurance company would normally sue your landlord and their insurance company to cover the loss.

Maybe find out if there are similar places where visitors rent short term.