Month to month leases plus revolving tenants-advice?

[Kathy Brasby]

We manage several rental units in our small town and were approached by our local meat packing plant a few months ago with an interesting proposal. They recruit legal immigrants to work in their plant and provide them with a housing allowance. They also help the new workers find housing. The packing plant pays the deposit and first month's rent on any units we can provide for workers. Because they also verify employment/pay scale plus run background and drug checks on their employees, that simplifies the process for us. And they promise to keep the units filled, which they do if a tenant moves out of the area. (And they have done so when we've needed them to, so that's not a problem.)

In many cases, we have multiple roommates sharing the rent but the lease seems mostly a suggestion to them. If one of the roommates doesn't like the job or the town, they just leave. Most of the time we have no forwarding address for them. We have made all the leases for the plant month-to-month. 

Today, I am meeting with a tenant who wants his girlfriend to move into the house after one of the other tenants moved out. Of course, I haven't been officially notified  of anyone moving out but he probably did. I think I'll just write a new lease (since the unit is month to month) and include the girlfriend (assuming she meets our criteria). I assume I need the OK from the other tenants who haven't moved out.

On Friday, I am meeting with a tenant from another packing plant unit. She is leaving the country for three months and wants to transfer the lease to her boyfriend and brother until she gets back. She signed a year's lease three months ago. (Before we started our month-to-month policy) Although I won't tell her this, I know I can't really do much about her breaking the lease if she chooses to leave the country. If I add the boyfriend and brother to the lease, can I charge a fee for the extra work of doing so? 

I would appreciate any ideas or suggestions regarding either of these situations and also if there are better ways to write these leases with revolving tenants.