It's taken some time but I think I've found plenty of information to help you fill in your gaps. Plus I can probably answer any additional questions now that I've researched this family in depth.
I've located many newspaper articles and other sources but I can't post it here. Could you send me a note to my personal e-mail so I can reply to you via your e-mail? Put the name McCullough in the Subject line and send it to email@example.com
I tried researching the McCullough childrens grandmothers and it seems the one you're referring to must be Annie Johnson McCullough that was born in Ireland. Is that correct?
I look forward to sharing more info with you.