Dear Ms. Thomas,
Thank you for posting your request on History Hub!
We suggest that you search the Louisiana Parish Marriages, 1837-1957 and request a marriage record search from the Parish in which Narcisse Lassai resided to obtain the maiden name of his spouse. As birth and death certificates often contain the mother’s maiden name, we suggest that you search Louisiana Birth Records and Louisiana Death Records for the vital records of his children as well. We also suggest that you review the FamilySearch Research wiki for Louisiana Vital Records.
We hope this is helpful. Best of luck with your research!
Found a possible family tree on familysearch.org. family search is a free website you just need to register to use.