You can go to guest services and trade in your paper ticket, for a smaller, like credit card size, plastic one. And usually, they have a pen at the turnstiles. for people that bought tickets for more than themselves. So that yes, to write a name on each one, to ensure same one is used by the same person. They still use fingerprint scanning to first get in, and also to use the train. So, yes, your ticket will be scanned before you enter the ride line for the train. That's where the backups usually start for that ride. And yes, park to park tickets are like Disney's hoppers, you can go back and forth between IOA and the Studios all day, and ride the train too, as you bought the park to park ticket.
We also keep our hotel key, and AP in a lanyard. I don't get my lanyard wet. When I do the wet rides, I wear swim shorts that have a zipper pocket. That's where the two card go. Otherwise, I like having the lanyard, as I don't have to remove either card from it, to work both the hotel door, and to enter the parks, and use the train. I tend to take it off, just to make it easier to scan, and so I am not leaning over the scanner.
And it does sound like you have live tickets. E tickets. But I am not sure why it would say credit card too. I can see asking for ID to ensure who the person is, but have never showed a credit card when having a live ticket at the gate. Give Undercover a call or send an email to clarify what you bought, an actual ticket or voucher to get a ticket. I find their customer service, quick and helpful. I have bought tickets, that were vouchers, and had to use the kiosks outside the park, to get my tickets. I used my credit card I used to buy the tickets, in the machine, after entering my order number. I haven't bought tickets from Undercover lately. I have had an AP for years, and just upgraded my kids to APs last year.
I hope you have a great time in the parks, the promotion deal is a great one, 5 days to enjoy much of the parks' fun rides, shows, themes and food.