GWramp,
Were you able to successfully sign in to the Apple ID and/or iCloud websites using the most recent Apple ID and password combination? Testing this out can help to confirm if the password and Apple ID are working well, or if there may be a broader issue.
The iCloud website may be found here: iCloud
If you're able to sign in successfully on the above link, try connecting the iPad to a different Wi-Fi network if possible, or try via cellular data if it's equipped with this. That'll help to rule out a network-related conflict.
Once signed in, be sure to check and see if text message forwarding is set up, which helps the iPad to send and receive the SMS/MMS (green bubble) messages. This page will cover the needed steps for that: Forward SMS/MMS text messages from your iPhone to your Mac or iPad - Apple Support
Automatically forward texts to your other devices
1. Make sure that you're signed in to iMessage with the same Apple ID on each device:
• iPhone or iPad: Check the Apple ID shown in Settings > Messages > Send & Receive.
• Mac: Open the Messages app, choose Messages > Settings (or Preferences), then click iMessage. Check the Apple ID shown.
2. On your iPhone, go to Settings > Messages > Text Message Forwarding.
If you don't see Text Message Forwarding, go to Settings > Messages. Turn off iMessage, then turn it back on. Tap Send & Receive, tap Use Your Apple ID for iMessage, then sign in with the same Apple ID used on your other devices.
3. Choose which devices can send and receive text messages from your iPhone:

4. If you choose a device that isn't using two-factor authentication for your Apple ID, a verification code appears on each of your other devices: enter that code on your iPhone.
Cheers.