1. He is an uncle on my mother's side.

Question

2. He is my maternal uncle.
[Can we use both expressions? Are both okay and the same? Which one is commonly used?]

3. He is an uncle on my father's side.
4. He is my paternal uncle.
[Can we use both expressions? Are both okay and the same? Which one is commonly used?]

Answer 1

Yes, all these expressions are correct.