ADVICE PLEASE: young renters not getting along

[Maria Matthew]

Hello everyone, I would love insight on how to handle this situation. I rent out 5 bedrooms individually. 

There are issues with two roommates, and would love insight on how to handle them. I also realize I'm the property owner, and I'm not there to parent them, but I do want to make sure they are happy (within reason) and protect my investment and also make sure they honor their lease

One roommate has a dog and is accusing the other of "disciplining", the other roommate is a clean freak and the other feels "attacked",  and bottom line there's just drama.

I want to know what the healthy line of mediation is, and basically I want to remind them that they're in leases so they have to be adults. Any advice is appreciated!