My son was given this worksheet. He wrote the word Jack in the lower right box and Garry above it in chart 2. I think he got it backwards, but does the sentence "Garry is my brother's Jack son" make sense? Why not "Garry is my brother Jack's son"? (I don't think the bottom left four girls can be identified exactly, either, but that's not the point now.)
I believe that "Garry is my brother's Jack son" might be wrong, although a lot of people say it. (I might be wrong). This is because the 's after a word indicates that the word has an "of" in front of it.
For example: "The king's horses neighed" means "the horses of the king neighed" "I was eating the man's biscuits" means "I was eating the biscuits of the man"
Personally I think the perfect way of saying it is "Garry is the son of my brother Jack" which COULD mean "Garry is my brother's Jack son" but "Garry is my brother Jack's son" sounds better.