Can the executor of the will force someone else to pay for the probate?

My step-father passed away in December. He crowned his oldest daughter to be the executor of his will. He had filed a will with an attorney several years ago, and it has to be probated. He and my mother were never legally married, but it stipulates in the will that he leaves the house and it's contents to her. She was going to sell the house to someone, but his daughter decided she wanted to buy it. Now, she has decided that she doesnt like the way my mother has treated her and has threatened to reposess our vehicles, which were in my step-dad's name, and informed my mother that she would send the will to her attorney to be probated, and my mother WILL pay for it. Can she force my mom to pay for the probate of the will? Does she have the right to take our vehicles? Thanks for your reply.