I assure you, I only did the account creation process once. The linking character thing was done pressing the big blue Import Existing Character button. Which called it as an error. Before this, my launcher had both characters. Now they are each in their own launcher.
You can replicate this I suppose by having two accounts on a launcher, opening both, going to the second account on the golden cape hunt, pressing upgrade account and then filling out the first accounts information in order to replicate this. That's all I did before the issue arrived and I've since taken some steps as suggested through the runescape discord in order to get on both.
As an additional detail can you please get somebody to fix this for me. I would like both on the same account. Otherwise the launcher has just become an even more annoying form of logging into my accounts.