You can absolutely go cheaper with Ting.
Because we are exclusively a pay-for-what-you-use carrier, if you're not using it for extended periods of time, we won't make you pay for anything other than our regular $6 per phone line fee.
For three lines, that's $18/month for us to park your phone numbers, and have access to our support team any time you need. Then, when you do come back to the states, just put your Ting SIMs in and when your wheels touch down, you should have service.
Porting the numbers is really easy -- you just need your Verizon account number and PIN. Then you'll need compatible phones (but with Verizon, your phones are probably already unlocked and compatible) and we'll take care of the rest.
Once you get the SIMs (shipped to a US-only address, sorry!), the numbers can be activated typically within a few hours. As long as the bill stays paid (with a US or Canadian credit card, or an Amazon Payments agreement), we won't cancel or suspend your service. We can even specially notate the account that you're using it to park your numbers for when you guys do come back to visit.
I also don't want you to overlook a perk you might have while living in Ireland on Ting -- that if you use WiFi Calling (no international roaming enabled with Airplane Mode on), you can use your US phone number to make phone calls and texts that only get charged regular Ting minutes rates. That is, you can call using your Ting SIM card in Ireland just like you were standing in the middle of Kansas -- no roaming or long distance. All inbound calls to your US number while your phone is using Ting WFC would be routed back to you, too.
It really couldn't be simpler for no-frills number-parking when you need it, and it can be WAY less than $125/month for 3 phones.