Adding guest to lease??

[Kevin Andrews]

Hi all,

Had a tenant request to temporarily move in her sister and what the process was for doing that. The apartment is in Rhode Island and  3 bedroom apartment. I have two adult parents living there plus 4 children, so 2 people per room already. The rent is currently 900.00 per month. Tenant said her sister would try to move out ASAP but may need until tax time next April. 

My thoughts on this is I'm OK with adding a tenant provided they go through a credit/background check and fill out an application. I was thinking about charging $50.00 extra per month for extra wear and tear and water usage in the apartment (I pay for water/sewer). 

My question is should I come up with an entire new rent agreement with the two current tenants and the sister signing it? Should I do an addendum to rental agreement and just add the sister on? I am currently on a month to month rental agreement with tenants and just want to cover all my bases because I've been in a situation before where I let one person sign the agreement and had her daughter and daughters boyfriend living there, and then the tenant who signed the agreement left and I was stuck with the daughter and daughters boyfriend which didn't last very long. 

Best way to approach this? The current tenants are absolutely great and I have no intentions of trying to get rid of them, but don't want issues with the sister in the future.

Thanks all