What happens to existing insurance coverage when Medicaid begins?

Mom has been on Medicaid since 10/18. She is a retired state (LA) employee & still has her Blue Cross insurance even though she receives Medicaid. Blue Cross EOBs still come in the mail. She also had Tri Care prior to Medicaid. My questions are: Does Medicaid affect the coverage Blue Cross & Tri Care provide? If so, how? Is Medicaid now the primary insurance w Blue Cross & Tri Care providing secondary coverage?
***I would ask Mom, siblings or Dad these questions, but they keep me in the dark. When I ask NH staff questions, they call both of my brothers. I was Mom’s primary care giver for 11yrs. Although she was primarily self sufficient, I was the only one there if she needed anything. Nobody else cared. Since Mom’s been in a NH, Dad & siblings have interfered with the relationship Mom & I had to the point she no longer speaks to me. These people showed up when money, property & inheritance was threatened by Medicaid. I’ve been there all along. I’m still here.