“It’s not going to be easy for her but at the same time what a fantastic moment it’ll be for her to see her sons playing out there,” the defender said.
“Maybe the best result for her will be a draw.”
“But we’ll be going all out to get the best result for ourselves. Whoever wins she’ll be happy in some respect.”
Paul, 23, is the world’s most expensive player, having joined United for $111m from Italian champions Juventus in August, and represents France, where he was born.
Florentin, born in the Guinean capital Conakry prior to his parents’ move to France, has been with French side St Etienne since 2012 and first played for his West African nation in 2010.
He says that Thursday’s match will be the first time the brothers, who grew up near the French capital Paris, have properly clashed on a football pitch.
“It’s going to be a magical moment and I hope we can both enjoy it as much as we can,” the 26-year-old said.
“We love sport and I have beaten him quite a bit at table tennis, but they’re the only times I can think of that we’ve played against each other.
“We’ve never played against each other or even with each other before in the professional game. It is probably because of the age gap that we’ve never managed to be on the same side.”
Normally a centre-back, Florentin has not been a regular starter for St Etienne this season but has recently settled back into the side at left-back.
Earlier this month, he told Europe’s governing football body Uefa that it would be ‘weird’ facing his younger brother.
“It’s incredible and rare so we are going to make the most of it,” he told Uefa.com.
“It will be weird because I will be marking him in a European competition. If I have to mark him, I’ll mark him with the same determination as any player.”
Manchester United manager Jose Mourinho agrees that the players’ mother will find the clash hard.
“It is not difficult, it is impossible, for the lady to choose,” the Portuguese said.
“I know from Paul that the mum wants a draw but, next week, one son will be happy and the other one will be sad.
“Paul is excited, Florentin for sure the same. So I think it is a good thing.”
Saint-Etienne are fifth in Ligue 1 while United lie sixth in the Premier League, where they have gone 16 games without defeat.
A third Pogba brother, Florentin’s twin Mathias, is also a footballer, playing for Sparta Rotterdam in the Netherlands.