Just remember, by saying each person needs their own card, and to use the same card both in and out, and all day (to get the daily cap) it is a bit more subtle.
A group can all use the same "credit card" if each have it loaded to their own phone or watch, or if each have a card issued in their name on the same account.
What you really want is each person to have a pay method, and consistently use that single pay method each time. So a card loaded on my phone, I use it to tap in or out each time all day. If you have multiple cards loaded, just make sure your favorite one is default.
Personal preferences aside, it makes no sense for a first time, one time (or even if you plan on returning) visitor to create a delay for themselves to purchase an Oyster card, load it, monitor it, maybe take more time to top it up, then take more time to recover funds, or worse, if you have over 10 GBP on there, then you need to deal with a lengthy process to recover the funds. Just tap and go.