Hi there! I'm been lokoking at tyou project and I have some comments to make.
First of all, it's impossible to send WhatsApp messages from any other app. Android has an strict security policy, so it won't be possile.
That was the bad news. Affortunately, I've an alternative for you. I've already started to develop a system that works with Web WhatsApp, so it emulates the keyboard and let you send WhatsApp messages automatically.
If you wanna know more about this, and how I'll implement it in your system, let me know via inbox.
Regards,
Hernan