Struggling to move past 'tapai' and 'timi'—how do I know when to drop the honorifics?

I’m a heritage learner trying to sound more natural when I speak with my relatives back in Kathmandu. I’ve been defaulting to 'tapai' for everyone, but it makes me sound like a textbook or a distant stranger. Does anyone have advice on the social cues for shifting to 'timi' without accidentally sounding rude or overly casual? I am asking specifically about learning Nepali, not a generic study routine.