This is meant to enlighten me more and educate me please...

It was something that happened between me and my brother that's making me scared, every time I keep clearing my WhatsApp message all the time I chat with some set of persons...

Aside a WhatsApp being linked to other device, be it laptop ... Are there other ways my WhatsApp messages can be read from other people, I mean what other means can someone be using to spy my WhatsApp conversation with people... Other than through linking devices...

Bigredmachine:
This is meant to enlighten me more and educate me please...

It was something that happened between me and my brother that's making me scared, every time I keep clearing my WhatsApp message all the time I chat with some set of persons...

Aside a WhatsApp being linked to other device, be it laptop ... Are there other ways my WhatsApp messages can be read from other people, I mean what other means can someone be using to spy my WhatsApp conversation with people... Other than through linking devices...

Very.. very possible. This happened to me sometimes last year, my conversations with my girl was being monitored through her phone by her ex.
It's done through a spyware, an app that is linked through her phone. But a friend told me that this app or monitoring spyware doesn't work on iPhones .

If you're sure you're being monitored by someone, I'll advice you rest your phone and reinstall WhatsApp on it, by doing so it changes the verification code.