I think my uncle's a cokehead
What makes you think your uncle is a cokehead?
We had a family gathering at home and I saw him hide a big bag of cocaine from my parents
It's totally inappropriate for your uncle to bring cocaine into your parents' home. You shouldn't bring illegal things like drugs into someone else's home. You should tell your parents about this so they can discuss it with him.
Nah, I'm going to cover for his ass.
That would be enabling his illegal activities; it would be a lot better to get him some help before he gets arrested.