How can I disable Siri for making reminders and calendar items? I would like Siri not to be able to make reminders and calendar items without asking for the lock screen password.

When I ask Siri to create a new reminder, I would like to ask it to unlock my phone first.
Your only option is to completely disable Siri when your phone is locked.

To do this, in the settings:
Click on General
Click on Passcode Lock
Scroll down and uncheck Siri under the heading ALLOW ACCESS WHEN LOCKED: