Just so long as the person who receives flight instruction (Transport (Passenger) Category C of A, licensed aerodrome etc) in your first example is the person who pays, then I'd say it's fine. The others aren't receiving any benefit in kind - unless, for example, someone asks for a trial lesson from UK to France and the 2 people in the back say "Thanks a lot" and go off on a week's holiday.......
Your second example is a bit less clear. If the person in the LHS is receiving legitimate flight instruction, then in my opinion that's fine - and you can be paid for your services as a FI. But if it's just a touring jolly with no form of instruction at all, you mustn't receive any remuneration as that would almost certainly be viewed as illegal public transportation.
It's probably safest (legally) for you as the FI to lay down the content of a 'trial lesson' - no-one could then accuse you of entering into an agreement under conditions required or imposed by your 'customer'? I'm no legal expert, but I'd certainly steer clear of anything involving landing at a different aerodrome with anyone who isn't at least a temporary member of your flying club!