Month to month tenant trying to sign a new lease before we close

[Jodi Campbell]

First time investor here! I tried the search function but didn't find anything. I apologize for my newbiness.

We are buying our first duplex. It is currently occupied on both sides. One is in a new year lease that started July at fair market value. The other side is month to month about 300 under fair maket value. Obviously we intend to increase that rent or terminate the month to month. It is currently being managed by a property management company. We just received their lease documents and they sent us an unsigned year long lease for the month to month tenant that begins the day after our closing date.

Can they do that? They are currently being managed by a property management company which we will not be using. Can we stop this lease from being signed? If it has already been signed but doesn't take effect yet can we basically void it? Can we back out of the deal since the terms of the tenants have changed? 

I am completely unfamiliar with how a tenant transfer happens and can't find a whole lot other than we inherit any current leases along with our tenants.  But thisblease doesn't start until after closing so is that an out for us?

Any insight would be greatly appreciated!