Pretty sure it’s true, but it’s just so……convenient.
I am constantly trying to picture how this one single car accident took all these parents lives, but I always end with Nozomu driving in like a mini bus with all these family members onboard, then crashing into a pole.
You're approaching it a bit too literally.
They don't have to all be IN the accident, just impacted by it to a significant degree. Some of these are obvious -- Niki had someone vanish from her life afterwards, Sara's baby daddy vanished from her life, Kaori was the last stabilizing influence on Yumi's early life when she got hurt, and the accident left her alone until she met Chika -- who is now pulled in (along with Chinami) because they're taking care of Yumi. Maki and Mokoto wind up having to help Miku recover from her trauma. Haruka sees her two best friends lives get turned upside down.
But honestly, a bus full of school kids in this story isn't unreasonable. Maybe there's a reason "school trip" is one of the things that echoes throughout the game. Maybe it was a bunch of students, teachers, and chaperones on the way to a field trip. It's possible, considering only a very small number of characters aren't a student, teacher, parents of a student, a much younger sibling of a student, or partner to a teacher. All of those people are likely to show up on a bus transporting students on a field trip.
But I think my first idea is the more realistic one. Something happened that caused 3-4 cars to collide in a horrific manner, and everyone we see in game is someone whose life was fundamentally altered by it.
