Well I can't help you with direct info. on your family, as I don't have any Robillard-Lamberts in my database, but perhaps I can give you some direction in which to look.
From what I'm gathering the line you're trying to verify looks like this:
Joseph Robillard Dit Lambert m. Scholastique Berard They had a son:
Leander Robillard Dit Lambert m. Sophie ? They had three children:
*Vittertin (Valentin), b. 1842, married Erntirne Courville in 1861 *Ambrose *Josephine
You said that Leander and Sophie's marriage certificate say that they were married in Berthier at St-Barthelemy.My first question would be...does the marriage certificate list their parents?Or what was the date of the marriage?Were there any sponsors listed?And the same for Valentine's birth certificate...who are the parents listed? Any sponsors?
Now St-Barthelemy is a relatively new parish - established maybe in the late 1820's (I'd check on that for sure though).Now if Leander and Sophie's son was born in 1842...they would have been married no later than 1841 or so.So that would put their births maybe around the early 1820's at the latest.I don't think St-Barthelemy's was established then.Now if you look in the PRDH (my subscription ran out, so I could only do a public access search) there are two other parishes in Berthier that were in existence before then - Berthier-en-Haut and Berthier-en-Bas...but there are no Robillard's or Lamberts listed at Berthier-en-Bas before 1799.However, there are many Robillard's and Lambert at the other.There was a Joseph Simon Robillard-Lambert that was married in 1796 at Berthier-en-Haut and had a son by the same name in 1798.This is probably around the time that the Joseph that you are looking for would have been born.There's lots of other Joseph's listed as well.Now because the PRDH only goes up to 1799 (although they're starting to add burial records from 1800-1850 - how exciting!), there is no Leander listed, as he was undoubtedly born after that.I guess if I was you, I'd order the church and civil records for that church and area from the LDS (www.familysearch.org) for that time period up to the late 1820's and see if you can find Leander's birth record (if the marriage record doesn't tell you who his parents are).
I don't know if that helps any, but if I can help in any other way, please let me know.