Help from stepmom about real mom?

Heres the deal. The real mom didnt want anything to do with Sam (my stepson) until I married his dad. He was 5. All of a sudden she decided she would get him and he would spend the night. Sometimes she gets him, sometimes she says shes gonna get him, and never shows. He goes 2 months sometimes w/o seeing her. I have to have him call her to have him talk to her. She wont say where she lives, just the city. She doesnt have a phone, we just know her work phone. Anyway, Sam is 7 now and it is still the same. We have a daughter, Chelsea, who is 16 months and were looking foward to halloween. Chelsea LOVES her bubba, and would love to go trick or treating this year with her bubba. The mom says its her year to get him, but I think no way, think of Chelsea. If she doesnt want him except for special occasions, she cant have him, especially on a day where Chelsea will be with him. What do you think? Am I right? I have a feeling my hubby will cave and she'll get him. How can I have him on halloween? Thank you for listening!