Another option is to offer the tenant an incentive bonus or 'cash for key' to move-out earlier than the 60 days.
Check with the terms of the lease and the purchase contract as well as the local landlord / tenant laws.
This matter will have to be spelled out in the Residential Purchase Agreement and agreed to by both Buyer and Seller. Consult with your Agent to determine how your offer should be written to satisfy both Buyer & Seller as well as to conform with Local & State rental/tenant laws. Good luck!