Can I turn off the alternate keyboards in Messages When I rotate my iPhone while in Messages, a totally different input area appears. I never use this, can I turn it off?
Assuming you're talking about the Handwriting Input panel in iOS 10:

Rotate the phone to show the input area, then tap the keyboard icon, showing the keyboard, and it will keep the setting. 



Image / info via: https://www.gottabemobile.com/how-to-turn-off-the-5-most-annoying-ios-10-features/