I didn't want to end up with the roommate situation where they're both on the lease, then one wants to leave and the other one doesn't want to, etc.So, what I did, was I kept the original tenant only on the lease. 

If your rental is a home with rooms you want to rent to roommates, perhaps you could rent the place to a nurse placement agency as corporate housing. 

She even let two roommates make their payments separately (not normally advised).The only thing to consider, that you may find to be a downside, is it can take several days to transfer the money to your bank account.

She ended up renting it to a couple of roommates, one of whom collected motorcycles. 

If your locality allows the difference, explain you misunderstood and consider "household" to be a single family unit, not separate roommates.

When I was in college in PA our landlord had a "no gun clause", but more than one of my roommates did not abide by this.

And city has been really tough on granting more units in this area based on past experience.I was advised to put a kitchennete instead of a full kitchen in the illegal unit, so it is not a "unit"; I was also told to sign a joint lease with 2nd floor - that this is a "roommate" situation"; I was also told to just to sign a lease on 3rd unit but let the tenant know/clear that this is a illegally unit and he/she willingly chose to live their.Any ideas? 

I had a roommate , similar situation , except we did it with real people , he didnt know I came home and had a group to play poker , when the noise stopped we cheered like hell .  

We also use passage sets and deadbolts, but in student houses, sometimes roommates {inadvertently} lock out roommates.  

I rent out 3 of the bedrooms to roommates.