I think I get this. In applying it for my own purposes, can someone please confirm or correct the following?

My assumptions:

Since both of my parents are now alive, by testing my father, if using both types of tests, I can get info on both his mother's MATERNAL line and his father's PATERNAL line;

I can determine data on my mother's MATERNAL line by testing my mother;

In order to gather data on my mother's PATERNAL line, I would need to have one of her brothers (or one of their sons) tested;

Questions:

To determine my father's paternal grandmother's line, who would I need to test? (I have not yet located any descendants from my paternal great-grandmother's siblings. Even then, I am only aware of her female siblings.)

Who would I need to test to correctly determine my father's mother's paternal line? Would that be a male descendant of one of my grandmother's brothers? (Although I don't know them personally, there are some out there that I could eventually make contact with.)

*For the record, in addition to my parents, I also have one sister and a half-brother (paternal).