The two siblings are expected to go head to head when the Ligue 1 club take on Manchester United in the first leg of their Europa League round-of-32 tie at Old Trafford on Thursday.
Florentin told The Guardian: "I watched the draw and, when I saw who we got, my first reaction was, 'Yes, that's a dream that's going to be fulfilled. [The whole family] will be in the stadium watching, including (Florentin's twin brother) Mathias, I think.
"We used to play every day and hope that one day all three of us would play together in a professional match. That was the biggest dream. We haven't managed it yet but having two of us together on the pitch is already good.
"We've been having fun about it ever since the draw, sending messages like 'Watch out, the match is getting closer' and so on."
Saint-Etienne, who recently beat Lyon 2-0 in the French top flight, host Lorient on Sunday.