Addendum to remove tenant, followed by rest of tenants canceling

[Gabriel Shawn Larson]

Hey BP and friends, 

I am in an interesting situation that I need some suggestions on. Just a couple days ago myself and the 3 tenants signed an addendum to the lease removing one of them as of 7/1. Today, the other tenants also heard their contracts are ending at work and are canceling their month-to-month lease with a 30 day notice. So I'm confident that the remaining 2 are responsible for Julys rent. What I want to be sure of, is whether or not the initial one that was removed is also responsible. I think its as easy as the fact that my addendum does not take effect until 7/1 and therefor he was currently a tenant when the notice was given and he should help pay July. Am I following the flow correctly? Is there anything I need to be cautious of in a situation like this? 

Thanks in advance for the help!

Gabe