I thought I had a list as to how the series should be read but apparently I don't? Anyway, here's the entire series in order. But if you don't want to read absolutely everything, you can just read these two and be done with the trilogy (but why would you do that?):

The Last Archangel: Redemption: If you're dead, you're supposed to stay dead. Especially if you went on a self-imposed suicide mission to save the world. Not that Tony'd know. The last thing he remembers is touching this giant tree in Afghanistan.

The Last Archangel: Ouroboros: Over the years, Gabriel thought he'd seen it all. But it seems that life still has some surprises in store even for archangels. Such as a dimension that none of them have seen before. But once awoken, some things can't be locked away. And some things are better left forgotten.

For the entire series, here's the info:

The Last Archangel: No one knows where angels go when they die, not even the archangels. And if one finds himself in a different universe after death? It's one thing to leave heaven purposefully, it's another to find that heaven isn't even there. And Gabriel is alone. 118,210 words

The Last Archangel: A Minor Christmas Story: In which Gabriel has forgotten it's almost Christmas, Jarvis has trouble with facial expressions, and Butterfingers is particularly fond of pink. 4,072 words

The Trouble with Emotions: There was no reason to be jealous of his siblings. He did not need the same things they did. His creator disagreed. 1,948 words

Welcome to The Twilight Zone: Time stamp for The Last Archangel. What happened to the Fantastic Four in Purgatory? 11,036 words

For Want of a Nail: Due to Gabriel's timely interference when Dean and Castiel challenge Dick Roman, they never go to purgatory. How does this change the events of the upcoming year? WIP 2/?

The Last Archangel: Redemption: If you're dead, you're supposed to stay dead. Especially if you went on a self-imposed suicide mission to save the world. Not that Tony'd know. The last thing he remembers is touching this giant tree in Afghanistan. 171,238 words

The Last Archangel: The Right Partner: Emotions were still tricky for Tony, but that didn't mean he didn't understand what happiness was like. And that he wanted it for Steve. 10,884 words

The Last Archangel: Four Aren't Better Than One: co-written with Alatar Maia. Even machines built by megalomaniacal evil geniuses could affect angels. It was just really, really bad luck that the one who managed to stumble into its path had a serious case of identity issues. 94,847 words

The Last Archangel: Not What He Seems: Five times someone realized Tony Stark was not what he seemed, and one time someone knew all along. 12,933 words

I Was Once Blind: ...but now I see. Gabriel follows through on a promise made, and certain individuals worry (or take offense). 7,312 words

The Last Archangel: Unspoken Regrets: co-written with Alatar Maia. One didn't live for as long as he did without racking up a lot of regrets, most of which went ignored. But after being split into four, Gabriel finds some regrets are harder to ignore than others. It's just as well that they're relatively easy to solve. 64,905 words

The Last Archangel: Ouroboros: Over the years, Gabriel thought he'd seen it all. But it seems that life still has some surprises in store even for archangels. Such as a dimension that none of them have seen before. But once awoken, some things can't be locked away. And some things are better left forgotten. 131,433 words

The Last Archangel: First Born: He just wanted to rest. But he was alive now, and he had no idea why. He had no purpose, no path to take. His brother had told him they had free will, the choice to do what they wished. But he was aimless. Who was he, if not Michael? WIP 4/7 chapters