Train tickets are different from plane tickets (where exact name matching is done for each traveler).
As you say, when you bought the train tickets, you weren't asked for the names of the travelers. That's because they don't care. Since your name is on the tickets, as long as you're one of the travelers, you'll be fine.
For some tickets in some countries, they can check ID to make sure the person who bought the ticket is using the ticket (to prevent two or more people using the same ticket). Even then, they only care about the purchaser, not the others on the ticket. In France, I had to show my passport with my TGV ticket.
In Germany, I had to have the credit card used to buy the ticket (they scanned the ticket, then swiped the credit card, and I was set). The ticket was for two (and cheaper than two individual tickets would have been); since only my name was on it, I joked that my mother was my "plus one" for the ticket.
For both France and Germany, the requirements were clearly specified on the ticket.
In Italy, they don't check either passports or credit cards on the trains. I don't know the rules for Norway, so (if you don't get a more specific answer here) check your ticket to see.