Welcome to the forum!
Unfortunately, the Family and Friends Railcard won't be of any use for you anymore as this only covers someone until the day before their 17th birthday (or its expiry, whichever is sooner). You can split tickets at Shrewsbury to save a small amount on the overall cost of the journey, but there's not much in it.
If you purchase both a Two Together Railcard for the two adults, and a 16-17 Saver for the 17 year old, you'll end up saving about £60 in total over the booking, even accounting for the cost of the Railcards.
The itinerary that would match your requirements would be the 0701 from Cwmbran direct to Manchester Piccadilly, changing there for a Northern service to Blackpool North departing at 1033. The return is effectively the same, but in reverse (xx56 from Blackpool North, xx30 from Manchester Piccadilly).
With Railcards
| Two Together Railcard | £30.00 |
| 16-17 Saver | £30.00 |
2x Off-Peak Return, via Hereford
Two Together Railcard | £72.50
£72.50 |
1x Off-Peak Return, via Hereford
16-17 Saver | £54.95 |
| Total | £259.95 |
Without Railcards
| 3x Off-Peak Return, via Hereford | £109.90
£109.90
£109.90 |
| Total | £329.70 |
Unfortunately, the 0701 direct train to Manchester isn't one of Transport for Wales' premier trains, otherwise I would have suggested potentially upgrading on-board to 1st Class and enjoying a restaurant breakfast on board! If you wanted to do this,
the 0459 and 1116 services from Cwmbrân are booked to operate these loco-hauled services (though these can change on the day), but that may not fit your schedule.
If you book through the forum's website, you'd need to do two separate searches: one for the 2 adults with the Two Together Railcard, and another with the 1 adult with a 16-17 Saver. You can add them both to your basket, and then checkout together.
The forum's website manages to drop the cost of the tickets further with a split at Shrewsbury, meaning the total cost with Railcards would end up being
£249.10.
FYI, the website that powers the forum's site, TrainSplit will also sell you Digital Railcards:
https://railcards.trainsplit.com. You should also be able to buy them from ticket offices, or from Rail Delivery Group or train operators directly.
Two Together search:
TrainSplit is a free service that makes it easy to find the cheapest train tickets for your journey.
tickets-beta.railforums.co.uk
16-17 Saver search:
TrainSplit is a free service that makes it easy to find the cheapest train tickets for your journey.
tickets-beta.railforums.co.uk