This is from a female. I received a proposal. And that person is asking my brother to create a whatsapp group so that he can ask me some questions. I did not accept to talk with him cz I feel uneasy. So he asked to chat with him in the presence of mahram on whatsapp group. Is this permissible
No, this is not permissible.
He can meet you and ask questions only once during the initial meeting in the presence of your father when he comes to see you for the first and only time.
If he has questions after this meeting, he can send them through his mother or sister.