Simon is the spastic, bizzare, sometimes overly-hyper twin sibling of Sidney. Even though they're genderbents of eachother, they both share somewhat different intrests and slightly different personalities. In future years, he becomes quite the flirt with other women, to either annoy them or to amuse himself. However, he's very loyal when he settles down with Lemongrab's genderbent, and loves her to death.
Before Twistdom was apparently discontinued, Simon had a "girly, childhood crush on his older, non-biological cousin, Aneles."
Everything below is LN
Lady Lemongrab (?)
(Lemongrab's Female Counterpart)
In Lemonnation, Simon is married to Lemongrab's female counterpart, as Sidney is married to Lemongrab. They are presumably very close, and probably do a lot of stuff together. Like that and not like that.
Prince Gumball: Unknown, most likely wants to rip his pink gummy guts out.
Lemonsoft's Genderbent: Probably is a protective big brother towards her
Taffy's genderbent: As said above, is probably very protective towards him and loves him 9999999.
Mayoral Job, Other
Simon most likely takes his job as mayor seriously. Much more seriously than Sidney does, and probably actually takes the time to keep his town in prime condition. He's probably a helpless hopeless romantic towards his wife, and will probably do a lot of stupid little things because he's a boy. He's probably just as much into clothes designing as Sid is, and looks up to Grace (Male in Japan, female in NA, NA Name: Gracie Grace) to get fashion tips.
In Lemonnation, Simon has a slightly different personality, forged by betrayal from his best friend Aneles leaving him. Becoming more serious and depressed, he has no good outlook on life most of the time, unless he's trying to talk people up desu. He believes he has no reason to live, so he just sits around his house, eating chocolate like a lady.