Tenants Gave Owner a Two Months Notice but Won't Move Out

My question involves landlord-tenant law in the State of: New Jersey.

Four months ago, my parents rented out their apartment to two people with help from a friend who works as a realtor. There are only two people on the lease, but the two tenants decided to move their boyfriends in permanently. My parents weren't okay with their boyfriends living there, so the tenants gave my parents a written notice at the beginning of February, stating that they're going to move out. My parents realtor friend made an agreement with the two tenants that she's going find them another apartment. And my parents had a written agreement from the tenants that they can show the apartment to other people. They showed the apartment to someone last week and that person is interested in renting it. They thought that the tenants were going to move out because they gave them a two months notice, so they told the person who's interested in the apartment that it will be available on April 1. Then, my parents called their realtor friend to let her know they found someone to rent the apartment and that she wants to move in by April. The realtor told them that the tenants aren't going to move out until they find an apartment. But the tenants gave them a two months notice and they want them out at the end of March. What can my parents do in this situation?

If the tenants don't move out as promised, your parents can commence eviction proceedings.