Morpheous = John The Baptist.
Trinity = The 3rd point of the Holy trinity, the Holy Ghost. She may die to save Zion or become pregnent, bearing the Saviour??
Seraph = Seraph means angel in Hebrew, indicating that he could be significant in saving Zion.
Persephone = Named after a Greek goddess kidnaped from the "over world" to be the wife of "Hades"
Niobe = Greek goddess who boasted to having more children than Leto. The gods slay her children (Children of Zion???)
I should have been more specific in my question - the brothers commented to several people that the three main characters were based or partly based on three living people. Unfortunately, I can't go into more detail because I haven't been able to get in touch with one of the "possible" three people. If there is enough interest I'll give out more details. I'm looking for Chicago references - I'll say that much.
Regarding the earlier insights, I agree - the characters are definitely a Joycian amalgamation.