Your Ellen would have been my James' "step-mother". My James Mobbs was 6 years old on the 1870 census record so it makes sense she would have been his "guardian" after his father, Aristarchus, died in 1879. James would have been 16 at the time. And Julia Newell was James Benjamin Mobbs' mother. So it sounds like the same James!
About Ellen... I do not know her maiden name. I can try to do some research aswell. I see your Thomas on the 1870 census.
Could you send a scanned copyof the documents you made reference to to my email? I'd love to see them. My email is email@example.com