I do not think Yamdev was being arrogant. He was doing what he always does - stand by his father! Shanidev always did his kartavya by his mother - so Yamdev took the decision to do his kartavya by his father. The person who loses is banished to earth - Yamdev decided to take that upon himself and protect his father! Indradev was very cunning, he got Suryadev's consent to participate in the discourse without informing him of all the conditions. Shanidev advised Suryadev to back off - but that would mean accepting defeat - so Yamdev decided to do his kartavya and prevent his father from banishment in case he lost.Sangya is not horrible - she thinks she has been wounded by Chhaya. She mistakenly thinks Chhaya seduced her husband and is pushing her son forward. She misunderstands Chhaya and thinks she wants to usurp her position as Suryadev's wife. So, she is giving in to anger and revenge.We do not know when Mahadev will publicly appoint Shanidev as Karmaphal daata - but it has to be soon as earth has come into being and will start being populated.