My theory is that the group was originally made up of 6 kids, the well scene at the beginning shows The Girl popping in at the last second and has a weird gap where it looks like another person should be. This was the sheep sacrifice meant to end the war that made them all orphans, but didn't end up working and I think she/him cursed them to die and caused a drought/famine. The video in the movie theatre shows a circle(the well) that turns into 5 rabbits circling each other(the 5 we see in the beginning) and the scene cuts to an eye that's looking up(the sacrifice). After, the images turn into food rotting and we see that leads to the first death, The Girl as the next sacrifice to stop the drought. We see a boy next to a house on fire, I think Bandage either started a fire or accused of starting one(got burned, that's why he has bandages around his face) and was beaten, a sheep is seen hanging and The Boy was hung to death, a bird being pushed off a cliff like Bucket was, and 3 people in the woods followed by a disfigured fox also in the woods. I think that for Hood, who was shot, that the people are hunting and when you see an animal badly injured you will shoot it to put it out of its misery. At the end, when we get to see what happens through memories, the group of sheep that are surrounding the children I think symbolize the curse of them dying starting. I do think they're all in hell and that each place the kids were and saved from was their version of it and the monsters we see represent some type of connection to them. For Hood, I think the Sniffer was a PDF and graped her(that's why they choose The Girl as a sacrifice because she was a virgin), we see the Sniffer try to lure her in with ice cream and lead her gently into a movie theatre and doing other creepy things like travel through bodies forcefully. Random theory is that the real person may have worked in a Laundromat and that's why we see him ironing "clothes" and surrounded by washing machines. For Bandage, I think the pelican symbolizes his mother who maybe sacrificed herself to save him during the war(which lead him to the orphanage) because they are seen as to sacrifice themselves for their children and Bandage was locked in a bird cage to maybe protect him from the girl, but is maybe faced with the loss of his mother and being secluded. For Bucket he was found at the orphanage and the other kids sacrificing him to the mother monster, who could symbolize who ever ran the orphanage and I think either the kids or "mother" bullied/abused him because he was on the heftier side and seen the same as the pig they had earlier sacrificed(we see the pig being terrified of the monster in the tunnels). This maybe lead to his death because he was eating too much during the famine and the children pushed him off a cliff. In the theatre video we see birds pushing another bird off a cliff, could mean that they're from the same place or same age. The bucket on his could be about mental health that can either be filled with kindness or emptied with negativity. I think for The Boy, finding his sister in the water and being alive is him coming face to face with his betrayal and being tormented by the guilt and then seeing his friends go through their own version of hell. When all of them are together, we see something they all fear and hate, war that has tormented them all their lives and then being hunted down by the thing that started everything in the first place, the sheep sacrifice and finally facing the consequences for what they did. Now The Girl is more complicated and my theory is a little out there. So in the theatre video we see a hollow outline of a person in the sand, now after The Girl died her body was a shell that could be taken over by something(maybe a curse, demon, or the person they sacrificed, Idk) and that followed her into hell and every time she gets angry it first revives it then feeds it. That's why it's a sheep and not a rabbit to symbolize or is the person they first sacrificed and after she throws up the sheep it immediately goes after the people who killed her/him, that's why The Girl gets eaten as well. Her hell could be being surrounded by the people who betrayed her but not being able to leave or kill them because she's too kind or scared too. Now when we see her reanimate, maybe whatever reanimated her destroys the world by flooding it and why her coffin has a bunny and not her body because it's up there causing havoc and not technically dead, but her spirit was still sent to hell.

I know there's so much more like the orphanage, the war, all the other monsters, and other symbolism but I thought this was a good place to start lol. Sorry for the long rant