Q. When buying a property which is not owner occupied, how long do we have to keep the seller's renter? We would prefer to lease option the property, rather than rent.
A. When you purchase a property with an existing tenant you must give a notice if you want them to vacate. 30-60 days is usually adequate but it may be dictated in some states.
If I were you I would consider leaving the tenant in the property. Holding costs are usually some of the highest costs in real estate and if you can keep it lower by keeping a tenant in place that may be a wise decision. It will also help you delay repair costs.
You can gradually raise the monthly rental and when they move out in the future you can move a lease option buyer in.
You may also want to convert the tenant to a lease option buyer.