It could be posible that yash is Bua's son and she had swapped him in place of Akash (Gayathri's son) and handed over Aksh to Radha (could be a nurse in the hospital where Gayathri gav birth to akash) who wanted to take revenge on SP for some reason. I think neither Yash nor Akash are Radha's kids. Now she wants to kill Yash so that no one will try to dig out the details about some secret she has hidden since 30 years.
Radh a could be MLa's sister or cousin who has seeked help from him to take avenge on SP. That could be the only reason, MLA was ready to get his daughter married in a days time.
Jaya