How do I ask my Khmer grandmother to speak 'naturally' instead of 'textbook'?

I’m a heritage learner trying to bridge the gap between the formal Khmer I study and the way my family actually speaks in Phnom Penh. Every time I try to use the polite particles or the formal script-perfect grammar I learn, they just laugh or look confused because it sounds like a newscaster. How can I transition from 'classroom' Khmer to the more casual, colloquial phrasing my family uses without losing the structure I’ve worked so hard to build?