The Handerson Fourgy was spawned from a bout of fandom madness experienced during the Glee spring hiatus. Macros popped up on tumblr of two Kurts in one screencap of Glee. The idea soon came about that this other person was Kurt’s identical twin, who shortly thereafter was named Cameron. Soon, Blaine also had a macro’ed twin, dubbed Everett, and thus the Handerson Fourgy was born.
Because the Handerson Fourgy is a completely fan-based entity, there is no set “canon” that authors or artists have to follow. Some prefer that the relationships between twins be strictly platonic, others want all four of them to engage in various types of group sex. Since each author or artist has their own head canon in regards to the Fourgy, readers and viewers should not consider all works to take place in the same alternate universe in which Blaine and Kurt have twin counterparts.