I'm incredibly confused on how this scenario works. I know there are 3 Act decks. If choose one to start with do I have to stick with it and then proceed to another or switch between them. And if the later is true if I start with the A/B and move to Act 2 do the other two decks have Act 1 removed or Just play everything in the order you wish to. Sorry if this isn't clear but that is how confused I am.

All three act decks are in play at all times (until completed). You can progress any of them whenever you meet the requirements to do so. If you've progressed to act 2A, you can choose to progress act 1C or 1E or 2A, in whatever order suits you. Progress on one act doesn't affect the other act decks (so if you progress to Act 2a, you don't progress either of the other acts at that time).

All in all, you might find it better to spread your efforts rather than just working on a single act until it's finished, because there are effects that get more dangerous the more act decks you've fully completed. However, later parts of the acts require more than just clue-gathering, and if you're not sure you'll be able to finish all three acts, it might be best to make sure you can complete at least 1 or 2 of them instead of spreading your efforts and not completing any of them.

Thanks so much.

Yes. Hindsight optimization on this scenario says: Try to advance all three decks and complete at least one.

Had to abandon one of the Act decks because one of the objectives turned out to be just too difficult to reliably achieve (multiple high willpower checks). We finished the other two but never recovered the relic.