We also need to know the dates of your May half-term
(I don't know about you, but we only get a long weekend in Scotland).
If you're quite flexible, you can get them £50-80 one way with your railcard. They're AP tickets, though, so you have to reserve well in advance
and ensure you travel on the trains you book for. That could come to less than £100 if you pick the right services.
Your next tickets up are your off-peak only savers, £139.90 RTN but you're really limited on your return services due to the off-peak only restriction.
The best site when using a railcard (particularly a family railcard) is the NXEC site, so give it a go for the dates your selecting.