The wide lapels, hair styles and facial hair tell me the gentlemen in the given photos are of the mid to late 1880’s period, maybe early to mid 1890’s. I see the examples you linked to the 1918 era, not a match. Close, but the subtle differences are there enough to tell. Coming out of WWII at around 33-37ish, your grandfather must’ve had your parent late in life as well as your parent having had you late in life? Not typical by any means, but not an impossibility I’ll agree.