Renting by the Room to Inherited Tenants

[Landon Fillmore]

I recently purchased a 4-plex, and one of the units is rented to a girl who has two roommates. The previous lease listed all three of the roommates, but they all paid separately. Now that I've inherited these tenants and am trying to establish a new lease, I am wondering how best to go about having multiple tenants in one unit who are not related to each other. Does anyone have experience with renting by the bedroom? Should I have each of them sign their own lease agreement, or just use one that has all three people listed as tenants? If they want to pay independently of each other, should the lease reflect that smaller amount, instead of the unit rate? 

Anything else I should consider? 

Thanks!