As noted earlier, you can't have the tablet Verizon Messages app syncing with two numbers at the same time. You can change which number is syncing on the tablet, but the app will only let you sync one number at a time.
You have to add a phone number from an active VZW phone line to sync the text messages to the tablet.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.
To set up a phone or tablet on your account:
Note: Messages start syncing on the day you sign up for Integrated Messaging. Any messages you sent before you signed up for the service won't be synced. The Integrated Messaging service syncs up to 90 days of messages between the web and your iPhone, tablet or other devices. Messages older than 90 days will remain on your phone, but won't be synced to the web.