How do I pretend to be Christian around my family while also setting boundaries?

So I’m obviously an atheist duh. To start off my family is hardcore Christians, my dad’s boss is actually a preacher, Mennonite. He once told my older brother that any music besides Christian music is a sin, and that really rubbed my brother the wrong way, even though he’s a Bible thumper with hardcore religious views. So I have a vague understanding of how my father’s boss is gonna be a problem for me. I already have a hard time holding my tongue and hiding my emotions. But fear of my parents reaction of my atheist views holds me back for the most part.

When I went to visit my parents my dads boss came over to pray away my father’s sickness. After he did that my dad’s boss told me that once I move into the apartment my parents and I have near my dad’s work, I won’t need to take any of my meds anymore. For context: I’ve now already moved into my parents’ apartment to learn how to drive because that’s an essential skill for me to breakaway from my family I can’t always depend on my parents I need to become an adult. I can’t always rely on my brothers to drive me around anymore either.

Anyways, what my dad’s boss said pissed me off so badly. I don’t understand why some Christians think I need to stop taking my essential medications. I need that medication, or else I’ll have physical and mental health problems. I’m just worried his boss is going to get even more pushy with Christian morals, which I don’t subscribe to. I’m also scared my family will start to catch on that I’m an atheist and disown me before I can get on my feet and become independent enough to move out. I don’t even want to eat at my dad’s boss’s house, because if I don’t, they’ll get suspicious. I could just say I’m antisocial, but I have a feeling his boss will say I have a demon in me.