He also trained his cousin Michel Lefrançais who he called his nephew. Michel married his illegitimate daughter Amélie whom Lalande then called his niece. Amélie and Michel became important members of the Lalande family team working day and night on many of his projects.
Siya rin ang mga sanay na kanyang pinsan Michel Lefrançais na tinatawag siya ng kanyang pamangking lalaki. Michel kasal ng kanyang anak na babae sa labas Amélie kanino Lalande pagkatapos ay tinatawag na kanyang pamangking babae. Amélie at Michel naging mahalagang miyembro ng pamilya Lalande koponan sa trabaho araw at gabi sa marami sa kanyang mga proyekto.