Me too!
My Great Grandfather is John Earl Sinclair (I was always told that he went by Jack) he was born later than the rest, 6 Jul 1903 in Perth, Ontario based on the birth record I found. His marriage registration said he was born in Woodham, Ontario.
He also had twins that they name Lindsay and Lindley (my great uncles) born in 1930. I wonder if the stories are confused… My Lindsay died at age 11 (1941) in a woodpile accident, and Lindley of alcohol related problems 1990ish, I don't remember exactly, but I was at the funeral.
I've seen a list of John Earl's older siblings and I did see a Lindsay born in 1896, but no Findley.
Do you have any sources or documents?
As far as William John Sinclair, I know he was married to Mary Margaret Wright, I have their birth record for 4 Jan 1887, in Hastings, Ontario.
Please message me back so we can sort though our info!