What should I call my girlfriend's parents, brothers and sisters when I go to her home for the first time?

You can call them uncles and aunts, or you can compare them according to your parents' age. If his parents are older, you can call them uncles and aunts, just like we do there! More cordial!

You can ask your girlfriend what customs there are, or how to shout them! What my brother and sister-in-law said was based on how your girlfriend shouted, so you shouted! Hey hey.

Bring things according to your own preferences, preferably according to the preferences of your family. You can discuss this with your girlfriend or ask your parents, which is the best, or follow the local customs! (It is best to discuss with your girlfriend)