Can I use one number on two different phone(Device) on Whatsapp? I just want to know if it is possible to have on two phones the same whatsapp messages.
The short answer: you can't do it using the native app, but there is a web interface that will work on Chrome, Firefox,  Opera and most other browsers  in desktop mode (i.e. "request desktop site" or "user agent: desktop").

Whatsapp allows only one device to pull your messages from their servers. You can make the app think you only have one device by changing the MAC address and some other files using root access, but that doesn't mean it will work.

Whatsapp messages are stored only temporarily on the whatsapp servers. This means thay when device A downloads those messages, device B can no longer see them. This means that, in order to keep your messages synchronized, you will need to constantly sync your messages using tools with root access. This is not very usable to most people.

The easiest solution would be to use the app on device A and the web interface, (web.whatsapp.com), on device B. To make this work on an Android device you need to make it request the desktop site. There you can scan a QR code into your first device by opening the menu and selecting "whatsapp web". Point your camera at the QR code and you can use Chrome to send and receive whatsapp messages.  This requires the device with the official app to be on and connected to the Internet.