Am I happy that the game extended its days. Anyway, here's the stuff for Jazz and Vader.
Jazz never decided to oppose Megatron. Instead he did his duty as Protector's Heir and was thus able to somewhat gentle Megatron's volatile ruling style. Because of this the great Cybertronian civil war never managed to destroy the planet. Thus Jazz never followed Optimus Prime on his search for the Allspark and never even learned of Earth's existence.
As he had no significant contact with organic, gendered species his views on inter-racial relationships are a tiny bit xenophobic, i. e. he is debating with himself whether loving Midvalley is something he really should be doing. He considers Midvalley still his third, though.
Darth Vader never strangulated his wife to the point of unconsciousness before he became angry at her in a fit of jealous rage. Instead he only pushed her away from him and started his duel with Obi-Wan Kenobi. The result of said duel are the same: he loses his legs and arm, he is drastically burned and he is stil the right hand of the emperor. What changed was that instead of being 'resued' by Obi-Wan and away from Vader, his wife stayed on Mustafar and found Vader's burned body. She stayed with Vader on the shore of a lava river and helped him stay awake. Sadly, the volcanic gases on Mustafar were not very healthy for the babies, which means that Luke and Leia did not survive their birth.
Darth Vader is still a Sith. He can still kill someone without batting an eye and has no scruples whatsoever, though he is significantly calmer because the 'betrayal' of his wife never happened.
Fifteen years after his children died, he became a part of the galactic rebellion against the empire. This Vader did not out of some kind of personal honour codex but because the emperor did not punish one of his courtiers whom had Vader's wife murdered in an attempt to break the Sith lord.
Darth Vader never went back to the 'light' side after he killed the emperor, but he also didn't follow the Sith way of only teaching one apprentice. In memory of his wife he re-opened the Coruscant temple and became a teacher for pilots.