I'd like to get back in touch with you and your sister and compare more notes. I'm almost sure we're discussing the same family, especially if you spoke to E.B. (Don't recognize the F.G., but perhaps I've spoken with that person as well? Not sure...).
IF I'm right about this being the same family, let me fill you in on a bit of what I know from records I've gathered:
You are right about Casimir being married before (Marie Louise Papineau dite Montigny) and having one son (Casimir) who died a month after birth. Marie died a week after Casimir was born, assumably of childbirth complications (she was only 16 or 17 at time of death).
Casimir remarried to Marguerite Laroche in 1841. They had at least 11 children:
Casimir, b. 8 Aug 1842
Marie Appoline, b. 28 May 1844
Narcisse, b. 17 Jul 1845, d. 25 Jan 1846
Joseph, b. 21 Oct 1846
Narcisse, b. abt. 1848
Pierre, b. 27 Oct 1850
Dieudonne, b. 03 Aug 1852
Simon, b. 01 Apr 1854
Isaie (Alfred), b. 25 Nov 1856
Hormisdas, b. 30 Mar 1860
Desire, b. 07 Apr 1862
On the 1861 Census record, both Casimir and Marguerite are still alive and still living in St. Remi. All of the above children are listed on that census except for the 1st Narcisse (who had obviously died) and Joseph, who, according to my family folklore, was in or around Ottawa at that time, working on building the parliament building.
According to Desire's baptismal record, it does not list either parent as deceased. I have searched the St. Remi record for 15 years after that birth, yet did not find any death/burial information for either Casimir nor Marguerite.
However, it appears that they did both die in the time between 1862 and 1871. There is no Guerin family in St. Remi in 1871, or anywhere else in Napierville. And I have found Pierre on the 1871 Census in St. Jacques, Laprairie on his own. His record does say that the parents were deceased.
Also, I did locate a Hormisdas Guerin in the St. Edouard 1871 census living with what appears to be an unrelated family as a "servant" at the age of 10. Granted, it's not proof it's the same person, but I've never found record of another Hormisdas Guerin besides ours anywhere.
Pierre remained in St. Jacques for at least 30 years, as he's still listed as living there on the 1901 census.
Narcisse married Rose de Lima Ste. Marie in 1877 in Ste. Helene de Bagot. Not long after the 1881 census, which lists his family still in Canada (place slips my mind at the moment), he moves to Biddeford, Maine where he dies young, around 1890.
Simon married Agnes Provost in St. Philippe in 1875 and stayed there for many years after (I believe I found them still living in St. Philippe on the 1901 census).
Isaie moved to Ontario, where he married Marcelline Droulliard in 1877. They later move to Michigan.
Joseph married Marie Rouille at some point after the 1871 census but before his first child was born in 1874. After Marie dies in early 1880, Joseph moves to Winooski, Vermont for work. He remarries in 1887 to Marie Foisy and brings his two children to the States from Canada, where they supposedly stayed with relatives in Trois Rivieres (don't know if the relatives were on the Guerin side or not). Joseph died in Burlington, Vermont in 1902.
That still leaves Casimir (the son), Marie Appoline, Dieudonne, Hormisdas, and Desire unaccounted for. I would assume it is one of them that went to California. I would absolutely love to know which.
Do you have any information at all who or even where they were in California? Do you know if that family stayed there? It would give me some idea of where to start looking.
Thanks for any information you can provide.