Well, sweetheart, I just saw what you think is fixing the situation. But stop and think about how Josiah joked, and how Zach joked.
Josiah's joke included the idea of his and Melody's two sons getting in a fight. He would not really expect that ever to happen, so it was OBVIOUS that Josiah was only kidding, NOT putting ANY real pressure on Mac. But when Zach said what he said about the development-age of the twins, he was in the middle of a conversation where he was talking as a doctor; so it was NOT obvious to Tiffany that he was joking.
Even so, Tiffany DID apologize to Zach for misunderstanding him. But Mac, who has LESS excuse to get mad at Josiah's joke, is allowed to yell against Josiah...and I still DON'T see Melody saying one word in defense of her husband.
If you and I were married in real life, would you let it pass when people insulted me, while being careful to defend some cousin of yours?