I do know that Michael Mulhern's father was Patrick Mulhern. That fact appears on Michael's 1915 death certificate. Is it possible that Michael and James O. knew each other...maybe related somehow?I don't know.I've never seen a sibling listing for Michael Mulhern.In fact, I'm not sure if his father, Patrick, ever came to Philadelphia.
I looked at the referenced copy of the 1910 census sheet. I noticed they lived on 4014 Ludlow street. Michael and his family lived at 2517 Olive street in 1910. Over near Logan Square, just east of the Museum of Art. So they were about 2.5 miles apart.
Oh well, that's all I know on this one. It's possible there's a relation here but not likely. Let me know if you find any other connections. Good luck.