Viji I think I did hv a reply here to your question which is quite valid 👍🏼
Its the way Yash was asked , He choose not to say ... The start was made by Gayatri and her exacts words which came out was "Kyun maar raha hai mere bete ko .. kya dushmani hai tujhe humare parivaar se " ... Why u r hitting my beta , what enemity u hv with "MY" family
This dialogue by Gayatri actually made Yash look like an outsider and Gayatri asked him the way as if he is some stranger hitting their family ka laadla beta .. Gayatri forgot Yash is their family ka laadla beta too
So the way Yash was asked , puts him off and he decided not to tell the reason when he is already made an outsider and its already assumed that AKash is the victim while he is the culprit
Instead Gayatri should hv asked the question in a neutral way ..something like "What happened ..why both brothers r fighting .. why one bhai is hitting another bhai" ... this question would hv auotmatically made Yash say it all
About Aarti not speaking up , here I assume she was too much scared after what happened to her in pub 🤔...
I do agree that Akash was not really at fault since he was too drunk there to notice anything but Yash I guess was expecting Akash to remain this much in his senses that he can at least protect a woman's honour ... Also Yash is sort of possessive for Aarti .. he did loose Arpita because he was second late to save her from dieing in front of his eyes ... in this case too he knew that its a matter of seconds ..if he was late , anything could hv hapepned to Aarti and that made him extremely scared and out of scare we see the extreme anger