iMessages on iPad sign in
When I go to either Messages or FaceTime the on/off button does not appear. All that's available is the Apple ID line, "Sign In" line (that does not work) and Create a new Apple ID line.
iPad Pro (2nd generation)
What do you mean by On/Off button? If you want to turn your iPads iMessage off, enter Settings > Messages > iMessage, and turn the slider off.
You need to sign into both iMessage and Facetime in order to use them with your iPad, this defines what Apple iD you are using for them.