At 12 and 14 I put my two on a train from Reading to Glasgow.
Standard class, seats reserved. Unfortunately at a previous station someone had put an old very frail lady in one of the seats I had reserved. I spoke to a guard, who said 'Just tell her to move' I didn't, but still fume at the moral blackmail exercised by the person who took her to the train and helped her settle. She went all the way to Glasgow, where someone came on board to meet her.
My two simply sat beside each other rather than opposite and swapped the window seat between them.
The journey required no changing and was trouble free. It was before mobile phones. However it was long and slow and when they returned, they said that if they had to do that journey again, they would choose to go to Paddington, tube to Euston and get a fast train from there.