I found some information that seems to be directly linked to the families you are researching.
In a newsletter published by the Cercle Généalogiques d'Aunis et Saintonge from March 1992 (p. 4), they published a list of names of mariner families in La Rochelle and included this:
Pierre Henry CHEVILLARD DE MONTESSON (1703-1748) x Marie Anne BOUDET, fils Paul CHEVILLARD DE MONTESSON (1748-1820), ship captain. --- referencing the book below:
« Dictionnaire de biographie mauricienne », volume 2 (issues 1-28); author : Société de l'histoire de l'île de Maurice; published by Esclapon, 1941; p. 1555
Then, I looked at GeneaNet and found this posted:
Paul Chevillard de Montesson
Né le 22 septembre 1748 - Rochefort, Charente-Maritime, France
Décédé le 13 avril 1820 - Rochefort, Charente-Maritime, France , à l'âge de 71 ans
Capitaine de vaisseau
Parents : Pierre Henry Chevillard de Montesson 1703-1768
Marie Anne Boudet
Marié 1) : ??
Marié 2) : le 21 octobre 1783, Port-Louis, Île Maurice, avec Charlette Fortin, Née - Rennes, Ille-et-Vilaine, France, parents : Michel Fortin x Nicole Marie Guy (Note: Her first mariage : le 1er août 1769, Port-Louis, Ile Maurice, avec Pierre Jean Moreau.)
Marié 3) : avec Elizabeth Bertrand †1820/
Note: As you may know, the Île Maurice is now the République de Maurice, or in English, called Mauritius. It is an island republic off of the east coast of Madagascar, that was a French colony until 1810, when it was taken by the British Empire. -- The records for the French period still survive in Aix-en-Provence.
The connections of these people appears very strong to those you are researching. You should be able to easily find the birth and death records of Paul Chevillard de Montesson online at the site of the Archives of Charente-Maritime that you have used so well.
- - - - - - - - - - - - - -
I looked at the original marriage record Pierre BOUDET and Geneviève MONTESSON (27/01/1710 : Rochefort St Louis (17) to look at the names you mentioned. And, I reviewed names in indexes of the Cercle Généalogiques d'Aunis et Saintonge, Généalogie.com, and two name dictionaries I own.
Based on all of these sources, in my humble opinion, I believe your names should be spelled FRIN and MONTESSON.
On all of my sources, I saw FRIN also transcribed as TRIN, so please keep this spelling in mind, and use it as an alternative during your computer searches. (I am confident it is an « F » because I have seen this name spelled in lower case letters in several places. Also, the final stroke, the tail, of a capital « F » hooks to the left, (a « T » hooks to the right). -- As for doubled letters, as in your name FRINN, it is a very common occurrence and when comes at the end, as here, it is usually an error.
According to my Larousse Dictionnaire Étymologique, FRIN is a contraction of FERIN, an old word in Gallo dialect (Ille-et-Vilaine) that means « savage ».
Regarding MONTESSON, in old parish registers, you will see the letters « D », « T », and « S » very, very, very frequently added to names that end with nasal vowel sounds. Trying to determine what is the correct spelling comes from experience, but even confuses the best experts. I often try several variations of spellings about which I am unsure at Geopatronyme ( http://www.geopatronyme.com
) to see what appear most, and where. -- You may want to try this when you are stuck as well.
MONTESSON (and variations) is an obsolete name today. Based on my Larousse Dictionnaire Étymologique, it comes from TESSON, an old Norman word for the animal called a « badger » (français = blaireau), which becomes fierce when angry or attacked; a name variation is TESSEL.
When doing searches, please remember that CHEVILLARD DE MONTESSON is an authentic variation of your name, and it is very likely that you will find some records during your research that will only record CHEVILLARD (instead of MONTESSON). (Note: Chevillard = « butcher » in English)
I realize that none of this information answers any of your questions (big smile!), but perhaps you will find this a little interesting.
Bonne quête !