Something is not quite right with the info somewhere likely.
The Neil that you mentioned b. 1865 in Linlithgowshire is certainly the son of a John Drysdale and Jane McNeil
https://familysearch.org/pal:/MM9.1.1/FQFW-F4F This Neil had siblings but not the ones you mention. His siblings look to be David, Margaret, Elizabeth and Jessie.
With possible siblings to the Neil you are looking for called Dugald and Catherine, there is this 1861 census entry:
James Ferguson 71 pauper b. Kilchoman
Mary Ferguson 67 b. Kilchoman
Dugald Drysdale 7 grandchild b. Kilchoman
Catherine Drysdale 4 grandchild b. Kilchoman
Mary Mccallum 3 grandchild b. Kilchoman
Address: Monenduich, Kilchoman, Argyllshire
Maybe parents of the Drysdale grandchildren weren't married. Not unusual to see illegitimate children going by the surname of their reputed father. There is this possible birth entry for Catherine
https://familysearch.org/pal:/MM9.1.1/XY5B-SXW and Dugald
https://familysearch.org/pal:/MM9.1.1/XTJQ-WMN Can't see how how a Neil connects to this family though. By 1871, Dugald is working away from the home of his grandparents, at the farm of an Angus McNeil in Colonsay and Oronsay.
Monica