I'm a W2 employee who might move closer to their parents to help them in their later stages of life. Their home is very small and located in California. I was thinking about building an ADU for me to live in to accomplish this. I wouldn't be the owner since my parents own the home and the lot that it sits on.

That being said, is there any chance that I could still get tax deductions for building this ADU?
Thanks in advance for any help!

Note: I was looking into the Short-Term Rental Loophole (e.g., rent it out for on average less than 7 days per a stay) and could definitely demonstrate material participation (e.g., designing/developing ADU, furnishing it etc.) But I'm not sure if I could take the bonus depreciation if I am not the owner of the ADU. Any help is much appreciated!