25M in NY approved for United Healthcare Community Plan but technically still a dependent under parents

For context, I’m helping out a family friend out since they’re not fluent in English. The friend in question (25M) was sick and in the hospital for ~1 month earlier this year. As he’s unemployed, his care was billed as a dependent on their father’s policy. However due to the nature of the treatment and some billing issues they got left with a massive hospital bill (like 100k+). The bill has since been reduced but in the months prior to that, someone recommended that they to apply for emergency medicaid (unsure if it was Marketplace or something else). That application led to the 25M being approved for UHC Community Plan with coverage starting October 1st.

Although we’ve been working to update the insurance on file with all of his doctors and gettings prescriptions to be transferred over to UHC, we think that some of his Rx refills in the meantime were sent & billed under his father’s dependent policy. Once we realized this we had the father get in contact with his labor union rep to help navigate the situation. Since the friend is still 25 the rep initially told us something along the lines of oh don’t worry, his dependent coverage will automatically end when he turns 26. Is this true? Or should we be worried of him losing his eligibility for UHC if he’s still under his dad’s plan and occasionally uses it? Do we need to remove him from his dad’s plan?

We’re currently in a limbo stage as we gather information but there doesn’t seem to be much about this topic. Sorry if this isn’t in the right place or doesn’t have the right flare, still relatively new to this subreddit. TIA

TLDR: Can a 25M have NYS Community Plan as a secondary insurance if he’s still technically a dependent under his father’s plan? Or should it supposed to be his primary insurance plan?