There are so many ladies there n Amba s house.
They could have asked Sai to stay there as one of the others to help her. As their sons colleague they could have helped her.
As per precap they agreed for the wedding i guess.
I think Satya will convince Amba and his family for the marriage. I still think it's an initial shocker where they want Satya to have a normal family which they couldn't have.
Amba bai turning negative will happen only after CN and Sai relationship reveal. She can become hostile to Sai Savi or manipulate Sai for her revenge. I am expecting the reveal to happen after marriage.