How to set up four Whatsapp accounts in Android smartphone with root permission

You may use the following apps for the purpose -

1. OGWhatsapp
You can use multiple Whatsapp accounts through this app. Best part is it does not require rooting.
To get it working, follow the steps below.
1. Take a complete backup of your Whatsapp data.
2. Go to your file manager and rename /sdcard/WhatsApp to /sdcard/OGWhatsApp.
3. Uninstall the your Whatsapp and install OGWhatsapp. Verify your existing Whatsapp and number on OGWhatsapp.
4. Install official Whatsapp for your other number.
Done!

2. SwitchMe
This app requires rooting your device. You cannot check one account when logged in to other account. Here are the steps involved-

1. Make sure your device is rooted and you have Whatsapp installed.
2. Install SwitchMe from https://play.google.com/store/apps/details?id=fahrbot.apps.switchme.
3. Create a profile on SwitchMe. Your current app settings for all apps will be saved here and this will be your Administrator account.
4. Create another profile from Create Profile.
5. Select this account and select Switch option. Your device will restart .
6. Install Whatsapp for different number than the one already installed.

The above mentioned apps may work and give you access to multiple WhatsApp accounts on a single device. However, please be aware that WhatsApp has been penalizing users for using third-party apps/programs for WhatsApp. This has begun ever since Facebook took over the reigns of WhatsApp.

Penalties include warnings and account suspension from 1 day to a month. So use wisely.