It *is* a bit scummy to charge £110 to print two tickets, but:
1. Ryanair's policy is clearly signposted at multiple points before, during, and after booking the flight;
2. This couple had ample time to print the correct tickets, as shown by the fact that they printed the wrong ones;
3. Although granted this could prove tricky for older people, they didn't even need to "print" the tickets at all, and could have checked-in online and downloaded the resulting boarding passes to their phone, or via the Ryanair App;
4. Even having got it wrong initially, it's surely part of anyone's pre-travel routine to confirm that you have definitely got the correct tickets and any other boarding documents (as well as everything else you need for travel, sorted if appropriate for ease of passing through security).
If this were small print in the T&Cs, which nobody can be expected to read in full, I'd have every sympathy. It wasn't. At some point, aren't customers also responsible for ensuring that they are aware of the rules/conditions of travel, and the consequences for breaking them?