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The fanfic in question begins with dear James and Lily Potter entering heaven and being surprised at how Harry survived. Heaven is like an extended township with Quidditch leagues and other administrative staff. They meet old Hogwarts founders and even play Quidditch with them.

Story was read on FF.net.

Then other dead characters begin arriving. They could see all the action from a large basin and even from their home which allowed them to see Harry at all times. First Cedric arrives followed by Sirius and other people who died.

The story ends with them having a massive viewing party on the day of the Battle of Hogwarts and how all the Marauders finally reunited.

I remember their being the mention of a lady with red eyes and white skin. Not sure why she was relevant.

After a bit more searching, a better match is "Above and Beyond" by ginnyjaffa.

The fanfic starts with James and Lily dying at the hands of Voldemort with the second chapter having James awaking in Heaven, here titled Above.

The first thing I realized was that I was lying down on something hard. I opened my eyes only to be greeted by thousands of twinkling stars in the night sky. I looked around and sat up slowly. I was sitting on a hill top, on a dirt path. Behind me, I saw a big shimmery thing that looked kind of like a moving curtain, or wobbly gates. The sparkles reminded me of a crystal.

Indeed, the houses have televisions which can view Earth:

"As I was saying, every house in Above—which is where you are now—has a small screen in their living room that shows the names of people who have just arrived to the people who knew them. The names come up in different colours according to how they die. So when your names came up in purple, we knew instantly that you both had been murdered. White means old age, green means sickness, blue means accident and red means you are going Below."

Cedric shows up a few chapters later, after James and Lilly are temporarily yanked down to Earth during the graveyard fight:

My mind was just starting to wander, when I heard a woman's voice from the isle next to me. "Cedric!" she scolded, "I know you just arrived a few days ago but stop moping at the floor! It's not going to be any help to you! Talk to someone about what happened last night for Merlin's sake!" she was still muttering when she walked out of the isle and I could get a good look at the boy following her. He was tall and well-built with blondish hair and he looked kind of familiar, but I couldn't put my finger on it. The expression on his face was sad. He was wallowing.

Sirius arrives in a later chapter, followed by Dumbledore in a subsequent chapter. And indeed, the last chapter before the epilogues has the three Marauders (sans Peter) and Lily watching footage of the Battle of Hogwarts, rejoicing, and James considering reforming the Marauders, maybe with Fred as their fourth.

I found it via search terms of "harry potter" "to heaven" cedric died quidditch.

Could it be Wizard Heaven by Iron-Flash?

James woke up with a yell of shock and looked around. He didn't recognize this place at all. It was a never ending cloud with a Quidditch pitch on the outside of a small town that was there. He looked around to see if Lily was there and sighed in relief that she wasn't. Maybe she held off the snake. He thought. A few seconds later a pop went off to his left and he looked over and saw Lily there and she started crying when she saw him. "I tried James! I did the best I could to hold him off but he just kept advancing!" She cried harder and James too her in his arms and held her there. "It's ok Lily. We did the best we could. Now the only thing we can do is wait. And possibly watch over our son some how… And hope that Sirius doesn't raise Harry as a little rule-breaking rebel that the marauders were in school." James said. "I think you just jinxed it James." Lily smirked at him while he just shrugged and picked her up. "Lets go check out our home honey. Hopefully Harry made it." They went to the house with their name on it and saw a little TV in the house and it was showing Hagrid picking up Harry while there was no sign of Voldemort in their house except for his cloak. "…I swear if Moldyshorts is out there streaking every one will wish they are dead…" James said with a sick look on his face while Lily rolled her eyes and watched as Hagrid took Harry to her Brother-In-Laws. "WHAT THE HELL IS DUMBLEDORE THINKING?! HE KNOW'S THAT PETUNIA HATES ME! HARRY SHOULD LIVE WITH SIRUS, REMUS, MINERVA OR ANYBODY THAT'S NOT HER!" Lily yelled out furiously. "Also…didn't we tell Dumbledore to stay out of Harry's life?" James asked.

Found with search terms of harry potter fanfic set in heaven