1) Are you supposed to send a congratulations card when people get engaged? Is that a thing? Particularly when one of them is your brother.
2) If you were cycling to Paris with a bunch of people and they were all raising money for charity, would you feel obliged to also do it for charity? I thought it was just a bit of fun but turns out there's a justgiving page. Feel a bit guilty asking people to give money for what is essentially a simple bike ride and a bit of a holiday.