Fleur was pregnant at the same time as Angeline, but Angeline had her daughter after the battle. Sirius died the same way, but had secretly been married and his wife had his child a year before the battle and died. This is the thing that I've changed. Hope you enjoy. :)
Polaris' dad died by the hand of his own cousin, Bellatrix. Sirius Black never got a chance to know his wife was pregnant. His wife, Eleanor Paris, died in childbirth to Sirius' son, Polaris, leaving the young baby to live with his second cousin, Andromeda Tonks. Teddy Lupin's parents died in the war and he too went and lived with Andromeda Tonks, his grandmother. Growing up without parents only pushed Polaris and Teddy closer. By the time they headed to hogwarts they were inseparable.
Teddy ended up in Hufflepuff, much like his mother, while Polaris ended up in Gryffindor, much like his father. Teddy was an metamorphmagus and werewolf, which was traits he received from his father and his mother. Polaris became a veela, much like his mother, and learned to be an animagus like his father. Despite being in different houses and being very different the two are best friends. Polaris is going into his final year at Hogwarts, while Teddy is going into his 6th year.
Neither Polaris or Teddy expected much this year. Teddy's godfather was Harry Potter, he knew everyone in that family, growing up with them, but he never really was much close to the kids like he was with Polaris. Victoire would be in her 6th year this year, while her sister, Dominique would be in 4th and her brother, Louis be in 3rd. Freddie would be in his 5th year, while his sister would be in 7th year with Polaris. Luna's twin sons, Lorcan and Lyssander, would be 5th years too. Despite these people being at Hogwarts with Polaris and Teddy, they never really thought much would happen with them.
Neither truly knew what was going to happen at Hogwarts that year, so of course neither were prepared for it.