Advice on renting to two non family members

[Kenneth Stump]

I currently have a tenant (military) that has been a great renter for two years. Recently his wife took a job in another state but his tour is not over for a couple more years. He has asked to let another military guy move in to help cover rent. 
 
The question I have is should I do two separate leases or put both on the same lease? Also should I consider any rent increase for this type of rental? Both are military and could get orders to leave at any time.