In English, there is no difference. Your uncle could be your father's brother, your mother's brother, or even your father's sister's husband or your mother's sister's husband. If you really need to make the meaning clear, you could say "my uncle on my father's side" or "...mother's side", or "my father's brother-in-law" or "my mother's brother-in-law", although those last two are also unclear.
For grandparents, it's slightly easier. Your father's father is your paternal grandfather, and your mother's father is your maternal grandmother. But normally we don't consider the difference to be very important, so we just say "grandfather" or "grandmother".
