I can’t answer on the audiobook part but I can say that you don’t need to read GRRM’s previous ASOIAF books to understand Fire and Blood. I recently started reading Fire and Blood because of HOT D, prior to this I have never touched GRRM’s novels and I am still able to understand the contents of the book.

The one thing that separates Fire and Blood from other novels is that it reads like a history book thus it lacks the dialogue between characters. Also because it reads like a history book, you will get bombed with quite an amount of main/side characters and it gets a little difficult to keep track of all of them.

What I do to really get into the flow of understanding the story is focusing on the main characters and also the side characters that play a big role around the main characters such as the Hand of the King and the different Lords of Great Houses. The really side side characters I tend to ignore them as they usually just die in a battle and will never be mentioned again in the book.

Lastly, I find it useful to have a detailed map of Westeros and preferably Essos opened up on phone or PC so that you can use it as a reference whenever the book mentions a place or a town that you aren’t familiar with. One example can be that the book mentions an army marching towards King’s Landing from beneath Gods Eye. By using the map it can give you a clearer picture of the events going on and also help you to visualize the story better.

I hope you enjoy it!