Why does my Russian sound like a textbook even when I'm just talking to my grandma?

I grew up hearing Russian at home, but I only ever spoke English back. Now that I’m trying to bridge the gap, I feel stuck using formal endings that make my family laugh at me for sounding like a news anchor. How do I start incorporating more casual, natural-sounding colloquialisms without feeling like I’m disrespecting the language or sounding overly academic?