So the pay as you go credit on your Oyster card can only be used for your own journeys and nothing else? I guess I could make do with contactless bank cards, but because I am bringing my friends on an outing, I am volunteering to uphold the entire cost of the outing. I guess I would just have to pay my friends back the cost externally?

Alternatively if they do not have bank cards and have to purchase the single journey fare, I can just pay the money out of pocket at the ticket machine before entering.