Even I used to think that.
Mansi is oblivious to most of the drama that happened so far and today, she was emotional about her son, so I dont expect her to understand this.
Kaku- I guess she already have doubts about her being jealous of Sai. She has been using this against sai. Only reason they/she don't question her is, to show infront of Sai that Pakhi is more samajhdar and she is nothing infront of her. Also, if they question her, wouldn't they be accepting what Sai said that day? They ofcourse dont want to do that na
As much as this seems shit, this is what I could make out from whatever I have seen so far