I am interested in selling my rental property but the tenants have only been there for 3 months. The only part of the lease that mentions selling is under lease renewal and states...

This agreement shall automatically renew for additonal one year term at a monthly rate determined by the Landlord giving tenant at least 90 days notice to rental increase, if the landlord increases rent if will be at fair market rate, unless terminated under specific provisions of this agreement or Tenant/Landlord elects not to renew this agreement. Notice of Tenant/Landord's intent not to renew shall be indicated by the Tenant/Landlord giving Tenant/Landlord written notice at least 90 days prior to the end of the present lease terms or any annual renewal period. Tenant agrees and understands taht for any reason to sell said premises, the Landlord will also give Teants at least 60 days notice and this agreement will be terminated and Tenants will need to vacate premises within the 60 days.

The lease will transfer with the property. New owner will be bound by the terms of the lease.

Bill [TX]

They only want to buy to flip it....

So the tenant is protected by lease and I am not covered by the statement about selling under Lease Renewal...

Leases protect the tenant. That is why owners do mo. to mo. or 6 mo. leases. 90 days is a long time to give notice.

why do lay people write lease provision that have no understanding of basic contract law?

Your lease provision that only allows you the owner to end the fixed term lease early if you sell IS not a valid provision under contract law, under consideration both parties must be bound by the terms equally, you can not have an early out of the lease and not the tenant for what ever reason its a two way street not a one way