Earth 756 is the mainstream universe for the Chaos Multiverse.
The Avengers Origins lineup includes only Captain America, Iron Man, Thor, Hulk, Black Widow, and Hawkeye. This storyline details the formation of the Avengers and their early adventures. It also shows them taking on HYDRA, and AIM for the first time. At the final Issue of the storyline they decide that they need a bigger force in order to protect the world, and starts recruiting heroes to become Avengers, leading to the Ulimate Avengers storyline.
The Ultimate Avengers
The Ultimate Avengers is one of the main storylines of Earth 756. The Avengers lineup here is much larger, however the main part of the Ultimate Avengers are the Origins lineup, Hank Pym, Wasp, VISION, and for a short while Titus. This focuses on their later adventures, one of the main ones included them fighting Thanos, which had it's own smaller storyline inside this series called Infinity War.
Infinity War focuses on many different factions fighting for the infinity gems, however the main part of it is about the Avengers fighting and trying to defeat Thanos who aquires all the gems, however even with the gems Thanos is defeated by the Avengers.
The Titus comics focuses on the character James Pit/Titus. A person with a black Iron Man suit, that also has both versions of Extremis' powers, and the suit is made out of Vibranium. Titus is mainly a villain, however in a limited miniseries inside of this called Titus Reformed, in that he is a member of the Avengers.
The Titus Reformed miniseries focuses on Titus' time as a hero. In the Titus Reformed miniseries, Titus is convinced by a mysterious figure to become a hero. Titus becomes a hero and eventually earns the Avengers' trust and becomes an official member. However in the last volume of the miniseries Titus is seemily killed, however in a issue of Titus after the miniseries ended it is revealed that Titus is still alive, and is back as a villain.