What are these number of sources? The most likely pathway is through ethnic variations like Elisapeta (Samoan, nn usually
Peta or Peka) or
Elspeth (Scots). It would also involved some rather complex rhyming manouveres which isn't terribly likely - most people find Beth-Bett-Betty-Tetty a bit of a stretch.
Is morphology being used to describe anything but a branch of biology these days? How strange. But I can see what you're meaning so oddly effective. The path of change that gets
Penny from
Penelope and Peninah is the English habit of shortening names from the first syllable. In Latin-based languages it's often a habit of shortening from the final syllable. So
Thomas becomes '
Tom' but
Tomas is often 'Mas'. My cousin
Penelope is '
Penny' in
America but the French cousins say
Lope a bit like
Lupe. And one uncle calls her Cantalope but that's another story.....
Devon