I have a retail store that has an apartment above it. The entrance to this apartment is from a stairway that is a storefront down. The owners of that building have 6 apartments the stairs lead too, plus my apartment. Somewhere in the history of the building an entrance was made to my apartment through a fire door between the 2 buildings. The previous owner of my building had lifetime rights to live rent free in my apartment. He since died. I am renting this apartment to my son now.

The owners of the store with the stairway say they don't want me to use their stairs. I told them that there is no other entrance possilbe for this apartment, but I would really try to think of a solution. They agreed. My son told me that they knocked on his door this morning and asked if we were making a new entrance (it really is impossilbe) because they were going to "seal" the fired door up. I doubt that sealing a fire door and the only entrance and escape to our apartment is legal. Is it?
Additional Details
This is THE ONLY access to this apartment. It was written into the abstract itself for the gentleman to have lifelong rights to live in our apartment rent free. There may have been another entrance at one time, but it has been this way for as long as any of the owners/ renters remember. One person said that about 50 years ago it was a two story furniture store, then the owner made an apartment above and the only access was throught this fire door. It even has the apartment number on the door, and a hallway right to it. So it has been this way for at least 50 years. We purchased the building with knowledge and being told this was the access. It is nothing new to the stairway owners.