It was very clear for me that Saw is Steelas Brother. His "Than make your decision." to Lux was clearly a reference to his Ahsoka vs Steela thought. Maybe Steela did not want to give away more secrets than needed to the Jedi and republic. Its just Ahsoka which looks very surprised when she hears that they are siblings. Lux and Ahsoka didnt know that. Ahsoka looking like, "Damn. i thought Saw is in Love with Steela and teases him because of his jelousy. But he teases him because of me and my immense crush on Lux which is noticeable for almost everyone, because i am the queen of beeing subtile???"