I have put the marriage of Charles Richard and Marie Poirier abt 1780 so that I can include them in the second part of the DGFA. It could be that they were actually married a little after that. The 1798 census of St. John's Island (which only became P.E.I. in the following year, 1799) shows Charles at the head of a family that then consisted of one male between 16 and 60 (himself), two females between 16 and 60 (Marie Poirier and the eldest of their daughters), five males under 16 (including Paul, who must have been born about 1795, because he was 64 when he died in 1859), and two females under 16. Charles and Marie thus had a child who was born in or before 1782 (sixteen years before the census), and so must have been married by sometime in 1781 at the latest.
Charles Richard was a son of Paul Richard and Marie-Renée Boudrot. He was born about 1751, and is listed as a one-year-old infant with his parents in La Roque's census in 1752. I have never seen any sort of record of his death. His wife Marie Poirier was a daughter of Pierre Poirier and Marguerite Girouard. This last-named couple is mentioned in the Cahier concerning the 37 families (p. 201), and the earlier generations of their ancestry can be picked up in the DGFA (p. 1332 for the Poiriers and p. 736 for the Girouards). I know of no record that would provide any clue regarding when Marie Poirier was born. As you indicate, we do know that both she and her husband were deceased at the time of their son Paul's marriage.
Charles's father Paul Richard was a son of Alexandre Richard and Marie-Madeleine Thibodeau (see DGFA p. 1380). His wife Marie-Renée Boudrot was one of the nine married daughters of François Boudrot dit Manne and Jeanne Landry (see DGFA p. 194).
By the way, the brother-in-law who was the witness at Paul Richard's marriage in 1819 was more commonly called Simon Aucoin, rather than Lecoin.