Even if they guess your screen lock passcode (unlikely in the six attempts they get to do so before disabling the device), they would need to know your AppleID password to disable activation lock. If you've used a good strong password for your AppleID, and enabled two factor authentication, then it is nearly, truly impossible for them to guess your password.
However, no, changing your AppleID password will not disable those devices linked to your iCloud account and activation locked - use https://appleid.apple.com to change your AppleID password if or whenever you wish to.
See Change your Apple ID password - Apple Support first though to be sure you handle your existing devices properly for a seemless change in AppleID password on them.
In terms of your stolen device, you sound like you did everything right. The screen lock passcode will keep them out of your stuff on it, and activation lock will prevent them from every restoring it and trying to activate and use it themselves.
One thing - if you receive any message - any message at all (text, email, whatever) that your device has been found, and asking for information from you - IGNORE IT. It is not a legitimate message and is merely someone trying to steal your AppleID login credentials. Apple does nothing at all about lost or stolen devices - they do not search for them, monitor them, log them or alert you about them.