There are many ways to install and use multiple Whatsapp on the same device.
Using GB Whatsapp:
GB Whatsapp is generally a mod which is created by app devs to mimic the use of Whatsapp. You may use this GB whatsapp along with the Original Whatsapp, and it also provides few new features that are basically not available in the original WhatsApp. This is the best feature of GB Whatsapp is of using the Always Online option to remain active 24/7 on Whatsapp.
Steps to install GB Whatsapp:
In order to install and use the GB Whatsapp, you have to first, download the package file.
You may then go to Security > then Apps > and you have to Allow from third party sources and then Check the box to proceed.
You may search for the APK file and then tap on it. You have to then click next and select Install.
After installing, you can open the app and then log in to your Whatsapp account
Use Parallel Space to use Dual whatsapp
In case your phone is not built for multiple accounts, you may also get an app called Parallel Space. Below are the steps to install Parallel Space on your device:
You have to go to Google Play Store, and search for Parallel Space.
Download and install Parallel Space.
Upon installing, when you open this app, it will then give you a list of all the installed apps on your phone.
You can select WhatsApp from there and then it will be added in the Parallel Space. You may then select WhatsApp, nine times.
And to use WhatsApp, you have to just tap on it to open, and use it like you are using the actual Whatsapp. You can then create an account.
Once you’ve set up the account, you can go back and open WhatsApp again to set up the another account.
You can then use two WhatsApp account simultaneously in your same Android phone.
Use WhatsApp Business to use Dual Whatsapp:
WhatsApp team has also created the WhatsApp Business which allows to set up another account while using a second mobile number. Above are the steps to add WhatsApp Business on Android phone:
You have go to Google Play Store and then search for WhatsApp Business.
You may download and then install the application.
Now you will have to set up your account using the second number.
You can then use two WhatsApp accounts simultaneously on your device.