I was in this exact situation.

If the current owner wants the sale and the tenant is in lease, he can give them a notice to vacate the premise and that allows 60 days. This can be incorporated in the contract terms of the sale, or you can discuss it with him, get him to do it and have the contracts exchanged under vacant possession.

We did it by getting the current owners to give notice and we moved in a week later.

FWIW - no one in a fixed lease is "safe" from eviction. If you are out of lease, 30 days notice is given, if it's in lease it's 60 days.

Good luck!