The only person I was successful in discovering anything about was the man at left. Mr. Ryan attended University of Illinois at Chicago during the 1930s where he studied business and accounting. I know nothing about anyone else whose names appear on these bookplates.
Neil McKnight seems to have a vague ring about it. It's possible he may be either a collector of note or someone in the book trade - a critic or bibliographer perhaps. A Google search, however, turned up zippo on him.
I've seen the Neil McKnight bookplate several times and they tend to turn up in science fiction and supernatural books. I can't remember which book this fell out of.