Hello again: The 1900 census shows Dennis living with his inlaws, and gives Oct 1879 as his birthdate, but this is puzzling because there is only a six month gap between Oct 1879 and April 1880 (when his brother was born). I suspect that Oct 1878 might be a better birthdate for Dennis (given that he was 2 years old in the 1880 census, whereas he would have been less than one if he was indeed born in Oct 1879.
Marion's parents were John and Margaret C Farnan, both from Scotland. They arrived in the US in 1872 and 1874 (Margaret arrived first) and were married about 1879 (21 years married as of 1900). The fellow I mentioned in the previous message has posted much more info about John and MArgaret's family online, and I suspect that he was related to Marion's brother John LAwrence Farnen, as he gives much more detail about that branch of the tree.

Best wishes

Norm