Colonel Jenna Cipher and AntiBronyBenSwolo are long lost twins
They are about are both are about the same age, have the same interests, and have the same style of posts. It's very much possible that they were separated at birth, to protect them. Just like Luke and Leia. SweetAI Belle is actually Claire Corlett
Claire Corlett wanted to interact secretly with fans, and write fan faction without getting sued. The name SweetAI Belle was chosen because it was conspicuous enough, but is a clue. This explains why Sweetie will occasionally reference being the character. Because they are!
Mystical Rainboom is actually supernatural
Because of their ability to change weather with emotion, predicting the future with uncontrolled cases of Deja Vu, bizarre nightmares and daydreams of other worlds, perhaps the word Mystical applies more than just for a name.