From "My Immortal: An Investigation", the author posits that all the misspelled names are relatives/friends/just have a similar name to the characters, and are being pulled into the story so that the originals don't have to show up.

Given that the fanfic analyzed was My Immortal, it reads like a free-for-all with everyone trying to get out of the story, and then getting dragged back when their names are used again. It's quite funny.

The writer also gives each misnamed character their own personalities and backstories. Frankly, it's much better than the source material (although that isn't too hard).