1. First take the full backup for your messages and data before going through OG Whatsapp:
2. Clear whatsApp data:
3. Go to /sdcard/WhatsApp folder and rename it to /sdcard/OGWhatsAp:
4. Uninstall Official WhatsApp
5. Install OGWhatsApp or Whatsmapp Solo
6. It will ask for your number. Give the old number which you have installed in official Whatsapp earlier.
7. Click OK
8. Now your OGWhatsApp or Whatsmapp Solo is ready for old number.
9. For second to use, go to play store and download official WhatsApp application.
10. It will ask for your number. Give the new second number and verify the second whatsapp.