Thanks for your reply, Sherrardk.
Just an additional thought:
When using the National Rail website, if you're not travelling alone it's important to click on 'More options, railcards & passengers' to enter the correct number of passengers. There are often savings to be made (even when buying 'walk-up' tickets on the day of travel) for
groups of people. For example, Arrive Trains Wales will give people travelling in groups of 3 to 9 people 25% off normal ticket prices after 0930 Monday to Friday and any time at weekends. Those reduced fares should come up automatically on the National Rail website if you've entered the relevant number of passengers.
Also, if you've not already got one, it's worth remembering that your family could make big savings if you buy a Family & Friends Railcard. (£30 for 1 year or £70 for 3 years):
http://www.familyandfriends-railcard.co.uk/
(Once again, the reduced fares should show up automatically when you tell the National Rail website that you've got a Railcard).