Why does 'aku' feel so awkward when talking to my older relatives?

I’m a heritage learner trying to reconnect with my extended family in Jakarta, but I feel like I'm breaking some unspoken rule every time I use 'aku' instead of 'saya' or family titles. My aunties sometimes giggle when I try to sound casual. What is the actual hierarchy for pronouns when speaking to elders in an Indonesian household, and how do I stop sounding like a textbook robot?