My New Jersey tenant signed a 1 year lease that ended last year and stayed in the apartment on a month to month lease. I am now thinking of putting the bldg up for sale. Is it important to have all tenants with signed leases when I put it up for sale? They seem to be dragging their feet on signing one. How do I get them to sign the new lease so I can sell it?

I'm not sure that you can force them to sign a new year-long lease, but I am pretty sure that you can tell them with 30-day notice that you will not be renewing the month to month lease. That might leave you with an empty apartment, if they decided to move instead of signing a lease. I don't know if that would make the situation better or worse for you.

If they are on a month to month rent merely give them notice they have to move. Then you merely make the apartment available on a lease basis only.