My regex skills are not as strong as I would like, but after a bit of research, I think I figured out a decent version, if you just want to match the possessive form of names:
(?-i)(\b)Eleanor('s)?(\b)
It doesn't work for names already ending in s that just get an apostrophe to become possessive. If you can easily switch between the two based on whether the name ends in s or not, you can use a very similar one for those:
(?-i)(\b)James'?(\b)
Writing a regex that matches the name, the name with an 's after it, and the name with just an apostrophe after an ending s is beyond my current skill. I'm sure it can be done, but I just can't make it work. However, if you're willing to allow just an apostrophe after any name, I think this works:
(?-i)(\b)Eleanor('s?)?(\b)
If you're wanting to have a single regex that works for possessive forms and contractions, I think it would be something like this:
(?-i)(\b)Eleanor
(?:'(s|m|d|t|ll|re|ve))?(\b)
I don't know if that's helpful, but I hope so. Either way, it was a good learning exercise for me.