Sultans actions make no sense but what do you expect from a gangster with poor upbringing?
After finding his mom, who had spent 30 years in a mental institution, he takes little time to spend with her so that she can adjust to life outside an assylum. What about taking time to develop a relationship and building trust and letting her get to know her grandson, Aryan.
From the way he mis-treated his son, Sultan's current behavior is no surprise.
He quickly barged in to stay in RK mansion with total disregard for its occupants. He is crude and totally insensitive to Radha. If Mohan K had betrayed his mom, it is no fault of Radha or RK - in fact they are victims too. MK is dead, one should let sleeping dogs lie.