Will I get full custody of my son, if or when she passes away?

My son’s mom has stage 4 cancer. We were together for 6 years before we separated and we were never married. My son is 12 years old, and we have a very strong relationship. I also pay child support and have the standard visitation rights. We don't necessarily go by the order. We basically share him so I get him often. My son’s mother and I have had a pretty good relationship through the years, mostly for our son, and also to keep things healthy. I absolutely wish no harm on her and I know it’s a very awful situation and I'm very sorry for her. I just need some answers because things don't seem right, and it’s hard because I want to show respect and support, but things are getting weird. Is there anything I should take care of now, like paper work or anything? I'm very curious about how this whole process could go. I don't have a problem taking my son full time. I have him just about every other day, and our relationship is very strong. I also have a wife that is very good with him, and a stepson that lives with me full time, we also make very good money and lead good lives. But there are somethings bothering me. There are a few problems I recently found out about, (1) My son told me that he goes days or weeks without seeing or speaking to his mom, and he’s very sad about it, he doesn't even get to visit her in the hospital. He just goes days and weeks without seeing her. (2) I am being lied to by her family and possibly her, for some reason, they say that my son’s mom is doing better, and they say she’s been resting at home, but my son said that they’re lying to me and that she’s very sick and in the hospital. He says she’s there for days and weeks at times. Why would they lie to me? I'm thinking that she is no longer able to care for our child. I wonder if they’re worried I will take him or something. I would never do anything to intently hurt her.