So here's  three simple method to access other whatsapp conversations.
{For Beginners}

1. Mac Address Spoofing (Level : Hard)

[But this need physical access of the Victim devices]

Ok here how it goes

MAC Address Spoofing

1. Whatsapp Uninstall
Firstly go to play store, search Whatsapp messenger and uninstall Whatsapp from your device. Make sure you that your Whatsapp account will completely uninstall from your android device.

2 . Get victim’s phone
Get the victim’s android phone which you want to access. You need the victim;s phone for few mints for the hacking process.

3. Find MAC (Media Acess Control) Address from the victim’s phone
We don’t know which OS platform is victim use. So below we give you all smartphone platform, with these you will easily find MAC Address from victim;s phone.
Android : Go to the setting > About phone > wifi MAC address
Iphone : Go to Setting > General > About > MAC Address.
Window Phone : Go to Setting > About > More Info > MAC address
Blackberry : Option > Go to Device >Device and Status Info > WLAN MAC

4 . Save Victim’s MAC address
After finding a MAC address, you have to save MAC address on the paper or where you want. Make sure you save right MAC address.

5. Find MAC Address of your own device
Get your mac address of your smartphone and save it for future when you want to access your own Whatsapp account.

6. Spoofing your mac address
Now you need to spoofing your Mac address.

7. Install Terminal Emulator . After installed  you have to change your MAC address with victim phone’s MAC address. By typing  $su and now hit Enter.

8. Now again type the below and then hit Enter. This will show you mac address for your confirmation.

                                               $busybox iplink show eth0
9. Now again, type the following command,
                                 $ busybox ifconfig eth0 hw ether XX:XX:XX:XX:XX:XX

10. Replace, XX:XX:XX:XX:XX:XX  with you friend/victim’s Android mac address which noted down in first step.
11. Now, you have successfully changed your Android device mac address. Now, you can confirm this by typing the following command,
                                                  $ busybox iplink show eth0

8. Re-install Whatsapp Messenger on your device
After Spoofing MAC address and Installing Whatsapp Messenger on your device, you can easily access victim’s Whatsapp account just follow a few more steps.

Open Whatsapp messenger and enter victim’s mobile number.
Now take victim’s phone for few second because after entered victim’s number, you have to get Whatsapp confirmation code from victim’s phone.
After getting code fill it into Whatsapp on your phone and delete confirmation message from victim's phone.