Our mother in law passed away. We gave her an iPad but we do not have the passcode to get into it.

The only option that you have to get into the iPad is going to be to follow the directions list here How to request access to a deceased family member’s Apple account - Apple Support without getting access to the account, there is no other way that you are going to be able to get the iPad removed from the AppleID to be able to gain access to it.