But they are not listening to me. They believe whatsapp will protect them. Escpecially my sister. She is not ready to switch to a different platform like signal or session.

When considering sms or voice calls (which here often used to communicate), those are insecure by design and unencrypted plain text communication.

Also contacting with teachers, keeping up to date about exams, everywhere everyone first asking for whatsapp number instead mobile number. I hate it. But we have really no control over anything right ? If the messenger we choose signal, session is empty then whats the purpose of keeping it in the first place ?