I have relatives (St. Martin) that married into the Wiltz families.
Alexandre Wiltz m. Amelia/Emelia Theriot (the sister of my gg-gm).

Alexandre Wiltz m. Agnes Hypolite (my gg-aunt)

Francois Wiltz m. Marie Mathieu
(my g-aunt)

I also have notes on a few other Wiltz families:
Hippolyte Wiltz m. Amelia NARCISSE (1869)
His parents were "Marcel and Adele". I believe Marcel was Alexandre Marcel (still searching).

There is a succession for an Alexandre Wiltz in St. Martinville (#1869, 1865). Not sure WHICH Alexandre this was, since the name was pretty popular with the Wiltz families.

However, I believe this Hypolite was the brother of the Alexandre that married Emelia Theriot.

I have more fragments of information.

I would suggest you see if you can get a copy of "Southwest Louisiana Records" by Rev. D. J. Hebert at your local library.
The church and courthouse records in this set of books should help you - starting with a known relative (born before 1910).

Death records are also helpful. You can also see if there are "Free" Death records online for your Wiltz line.