Can you tell me please where Margaret Quayle appears in the official records for George Watson? Was she given as his mother on his marriage or death cert?
Who was given as his father on the same document?

I still haven't worked out why you are so sure he wasn't the son of James Watson and Catherine Quirk if he was living with them in Michigan in 1887.
Do USA censuses have him as their adopted son, or as their son?

Thanks if you could give more details.

Sue