I have heard of that clause where a person is allowed to live in a house or apartment for the rest of their lives, while not outright owning the property. It is seen by some people as a 'middle ground' between the interests of one family member vs. another.
At least your father's new Will lets you live in the home for the rest of your life. Obviously getting the deeded property would be ideal and is what you expected, but I'm thinking that things could be worse. How well do you get along with your stepmother? For how long was she married to your dad?
I understand your fears about the possibility of your stepmother ceasing to make payments or to evict you. (I'm in a similar situation myself. My dad bought me a house as a gift 20 years ago, and then I found out that in his Will he had left shares of the house to both of my brothers to avoid the estate tax. One brother wants nothing, but the other brother is making my life Hell.)
I'm not a lawyer, but I think that the clause letting someone live in a house for life means that you do indeed get to live in the house for the rest of your life. You'd have to see an attorney to find out exactly what your rights are. Maybe your dad deeded all properties to your stepmother, but made sure to put in the clause that you can live in the apartment for the rest of your life as a way of protecting you?
Do you think for whatever reason your dad may have changed his mind about allowing you to inherit the property? When my dad bought me my house as a gift, he also used the excuse of 'business' and 'tax' reasons for not putting the house in my name. The house was a 'gift', but was always in my dad's name. A lot of parents want to retain control; hence, they never actually 'gift' the house to their child.
I think the clause is called 'lifetime occupancy'? So you wouldn't own the condo or be able to sell it, but at least you could live there for the rest of your life. Maybe your dad decided this would be best for you, in his mind? Some parents want to keep things complicated, even in death.
I guess the biggest concern would be figuring out just how much (if any) leeway your stepmother might have. Is your stepmother the sort of person who might deliberately try to sabotage your situation, or does she seem to be okay with you living in the condo? I would definitely see an attorney, just to determine what your rights are in this situation.