Tenant having family stay for two months

[Alton Blake]

Good afternoon everyone!

I live in Boston MA. And have a tenant that just informed me Friday that his sister and her family( two adults and three kids) was going to stay with them for a couple of months. The family under the month- to- month lease already have four people living there (two adults and 2 kids ). I was thinking of drawing up an additional agreement ( MTM agreement states to have a written agreement if persons are there more than 1 week) stating dates of arrival and departure plus $200 extra ( the time they are there) to cover water expenses. Any thought or insight would help.

Thank you,

Alton