I have read the three mangas and I honestly don't know how it will be stretched to 12 episodes

I’ve been reading it, and yeah, I’m not sure. There’s an ongoing sequel, so they might adapt some of that… Idk. We’ll see.

well lots of fillers and maybe the movies they shoot in the movie club can have a detailed plotline of its own. Basically a story within a story.

i am kinda hoping that they include the story of other couples too

eu estou torcendo para 2 season desse anime

I think they will def include all three couples' stories in this so that will def help (or at least, I hope so, cuz ima be pissed if they don't animate Ichikawa's story). But I don't think they are gonna include anything from the sequel story because it jumps into the future a bit.

This is just an example, but I'm pretty sure the first season of Given only included the first 4 volumes, so it may not seem like it was a lot, but if they do it right, it won't seem super stretched out. Or at least, I hope so.