Former Brazil international Mazinho says he has no preference as to who wins between Thiago's Bayern Munich and Rafinha's Bayern Munich on Wednesday.
Mazinho's sons could meet in the first leg of the sides' UEFA Champions League semi-final at Camp Nou.
Rafinha has featured more often off the bench in Europe for Luis Enrique while former Barca boss Pep Guardiola has regularly called on Thiago since his return from injury.
However, Mazinho says it is more a case of pride for him, with the World Cup winner telling Perform: "I support both, I sit on the fence. For me, without any doubt it's a huge source of pride."
With Thiago's contract due to expire in 2017, the former Celta Vigo midfielder also said his son may be offered a new deal at the Allianz Arena.
"About this [contract] issue, I have no idea. I have my player there, he is not just my son, I'm his legal agent," Mazinho added.
"When you have the opportunity to play with the manager who brought you to Germany it is important and I want his new contract. I believe they can renew the contract. I hope so.
"Thiago has a unique quality. In my time as a player, I was different, even in the same position. He's a midfielder with great technical skills, and when playing one on one he has an easy solution.
"He's more creative and I was more defensive but with the ball I used to play well. Thiago has these skills, he's defensive as well and know how to play one against one. I don't have this ability."
