Hey Jeffrey!
Definitely listen to Debra Regan's advice about adding "jointly and severally" to the lease. I have multiple rentals with co-leasees that either don't know each other or know each other and are co-habitating. Anytime you have more than one person's name on the lease, especially if they are younger people - things can go awry very quickly and a solid lease can help you nip arguments in the bud. In general, the best way I've found to cut down on the co-tenant shenanigans is to have them sign separate leases (if they don't know each other), OR have them sign a joint lease (if they do know each other), but allow them pay separately. This has worked beautifully for me over the years. So from a rent collection perspective, if I have tenants on a joint lease - I "treat" each person as if they have their own lease, but with 50% of the liability. This is also true for couples - never make the mistake of assuming that a couple (especially if they are not married) is on the same page, financially.
So how would this work, you ask? Let's say rent is $1200, the late fee is 10%, and there are 2 tenants on a joint lease. I charge tenant #1 $600, plus $60 for late fees. And the same for tenant #2. Luckily for me, I use Dwolla to accept payments, so I just have the tenants set up their own accounts and that usually works out pretty well.
Now, there will be situations beyond rent that will require cooperation from both tenants, and you can treat payment and communication between the tenants the same way.
Example 1 - fines for tenants on a joint lease:
Say you get fined by the city for recycling incorrectly. I will normally charge the tenant a fee in the amount of the fine. In the case with tenants on a joint lease, I would invoice them separtely, but cite the full amount on both invoices, always naming both tenants in the citation as being jointly liable for the charge.
Example 2 - evictions for tenants on a joint lease:
Lets' say you have one tenant who hasn't paid in 2 months, but the other tenant is. Unfortunately, you will need to evict BOTH tenants as per laws in most states. In situations like this, its unfortunate for the paying tenant, but there are things you can do make the situation suck less. One thing I've done in the past is let the paying tenant back in under the stipulation that they must have a qualified co-tenant available to sign a new lease OR they can sign a new lease for the full rent amount.
Example 3 - breaking the lease for joint tenants:
Let's say your tenants have gotten to the point where they simply do not get along. Arguments and fights ensue, your neighbors are complaining, and now you are getting calls from one tenant complaining about the other. The solutions might be to give the tenants the option of doing a a lease reassignment. This only works out well of one tenant want to leave and the other wants to stay (which is normally the case). Lease re-assignments can be stressful, but there are ways to take much of the stress off your hands as a landlord. What I usually do is put the responsibility in the tenant that wants to leave. She/he must find a qualified tenant (who will accept to pay the partial security deposit and an application fee). Then once they have found someone, I do my due diligence, make sure the new person has met the current roommate, and have them sign the necessary paperwork. It's always imperative to let the tenants know that until a reassignment is finalized, they are still liable according to the current lease for all rent and monies due.
TLDR; Only do joint leases for tenants that have had a relationship prior to lease signing, and always allow tenants on a joint lease to pay separately, even couples.
Hope this helps in some small way!