Bonjour Marie-Claire!
I have yet to establish the relationship between James Ponisi (1813 Madron Penzance) and Dominick Ponisi (1820 Devonport)- perhaps cousins?

I have found that James (1788 Italy) and Mary Newton (1790 Penzance had another child in addition to James (1813), Marian (1824) and Rosina (1827); he was William Ponisi b. 1815 Stoke Dameral, Plymouth, who married Angelina Rivolta 1839, Plymouth. He died abt Sept 1889 Barton Regis.

I would be happy if you were to see if Ponisis were to be found in the Channel Islands. Thank you!