Different lease for term lease vs month to month lease

[Houston Groff]

I am closing on a duplex in a few day where one tenant is 3 months into their 1 year term lease which according to my state law I must honor till the lease expires. The other tenant has been in the home 9 years and is on month to month terms. My question is, can I have the month to month tenant sign my lease agreement even though the I am assuming the previous landlords lease agreement with the tenant who is in their 1 year term. Does this violate any fair housing issue with using 2 different leases with different terms in the same building?