How to address your relatives
The Chinese have a very specific way to address each other depending on how they are related. In general there is a specific name for the relations thru the parental and different thru the material side. There are a lot of variations, and this video gives you a great introduction. https://www.youtube.com/watch?v=A1HaZ4WLo50
There is one exception with the word 公 (Gonn). This can be used specifically to address an elder male – the father of your mother. However it can also be used to mean someone very old or have already passed away. This is common to see this word in grave stone, after the surname eg 周 公 Chau Gonn.
It is also common to add a sequence in front of the salutation. 二叔 (2nd Uncle) 二姑婆 (2nd Aunt). Thus signifies the sequence of birth for male and female side of the same family. Therefore it is possible to have a 2nd Uncle and 2nd Aunt, as there were four children in that family.