Roommates

      
      When more than one people sign the same  lease or rental agreement,  they become cotenants and  have  the same rights and responsibilities  about the lease.
If one of cotenants (roommates) doesn't pay the rent or  behaves in a way that is against the lease, it affects all other roommates' tenancy.
        Negative actions of one cotenant, such as damaging property, gives landlord legal to terminate the lease with notice. In practice landlord usually keeps the good tenant if he pays the full rent on time and doesn't exhibit offending behavior. 
         Paying the rent: Roommates may decide to split the rent the way they want, but this doesn't affect their relationship with landlord. If one of the roommates can't pay the rent or disappears, landlord can collect the full amount from the rest. Also landlord may insist on receiving one single check in the full amount, if it is in the agreement.
         Roommates  may  have informal agreements  about  splitting shopping and rent cost, music volume, late night  friends, cooking, cleaning dishes. It is not landlord's business to deal with such things. If things go to court, judge  can only
enforce financial agreements between rommates. To avoid future problems and
misunderstandings, it is best to have a written agreement from the beginning.
         Roommates can't  evict eachother. Only landlord can. (There are a few exceptions to this rule).
          If one of the roommates want to leave before the lease ends, he should
get permission from the landlord or find another person who is acceptable  to the landlord.  Simply leaving can have serious consequences. Then landlord can evict
all occupants. Usually in such cases  landlord  the rest stay, as long as  monthly rent is paid in full and they are not problematic. Any new roommate needs to be accepted through application process, unless lease agreement  says otherwise.
         If a new roommate is added with approval, probably monthly rent and security deposit will increase.