More About George Thomson
The whole Thomson family heritage, by which George as the eldest son would have been most influenced, is in The Thomsons of Durham: Tom Thomson’s Family Heritage. The additional small book on The Two Talented Thomsons provides some more information about George’s successes as an artist.
And, you’re quite right, George is not given enough credit for his substantial and accomplished oeuvre. His works are both in the National Gallery and the AGO. Although there is no George Thomson archive, the Tom Thomson Memorial Gallery in Owen Sound did a show on George for which they printed a newspaper supplement with good information about George. The most authoritative sources on George are his grand-nieces, one of whom, Helen Young (pictured on the back of the Thomson family book) painted with him and wrote a niece piece describing his palette. Helen’s sister Kay (also pictured) is the family historian and has many charming stories about George as well. Both Helen and Kay were extremely helpful during the preparations for the catalogues and book.
One of the panels for the Durham West Arts Centre exhibition compared where George and Tom were at various points in their careers. There is no doubt that his oldest brother’s decision to sell his business and decamp to New York to take art lessons at the Art Students’ League was a huge influence on Tom. If his lawyer/business owner brother was prepared to throw all caution to the wind to become an artist, when he had no art training, why wasn’t Tom doing more? I develop this idea in my article, “Tom Thomson’s Toronto” which reveals a great many unknown facts about Tom’s seemingly lost decade in Toronto—especially on the seven years before he discovers Algonquin Park.
You’re definitely on the right track to hone in on George. I would look at "uncle" Brodie as well. Joan Murray has shed some light on William Brodie (as have I in The Thomsons of Durham) but there is more there. There’s also a link/influence to Ernest Thompson Seton that is fruitful for exploration.