Landlord sell the renter's house

[Tracy Percival]

Hello everyone,
My brother and sister inlaw are renting an entire house in NJ, and have been for the last 3.5 years. I rented this same house for 10 years prior to them, before purchasing my home. The Landlords are an older couple and were absolutely awesome when I lived there. Since moving out, the husband developed alzheimers and now everything is being handled by the wife who is not use to handling the landlording, and also seems now to have medical problems.

She told my brother and sister in law that she needed to sell the house. They made her an offer on the house and she never responded their offer and sold it to someone else (for 20K more than their offer) and is now demanding that they leave within 30 days. She never countered their offer. They signed their 1 year lease only at initial occupancy. I am sure they have a similar lease as I I had, which stated that after the 1 year if not renewed then occupancy would be continue month to month thereafter.

what is the time frame a landlord must give a tenant to vacate in this situation?