I want to make a return journey from London St Pancras International to Ashford International using Southeastern High Speed. Two adults, two children, with a Family & Friends Railcard. Outward on Sunday 3 April in the afternoon, back on Wednesday 6 April in the afternoon. I don't want to be tied to specific trains. I'm seeing very different prices from different retailers, perhaps around weird treatment of Southeastern's Kids for a Quid offer. Can anyone please recommend what I should buy, what the price should be, and where I should buy it?