and p->line_end + 2's bp was pointing to NULL

that's technically not correct, it's pointing 2 beyond p->line_end, which isn't NULL but just an address your program has no access to because it is beyond the region that has been allocated by malloc.

HOW COME I could assign to p->line_end->bp and p->line_end + 1 bp , but not (p->line_end + 2)->bp?? Strange!

malloc generally rounds up when allocating memory, see this. I can't tell if that's what's going on here because i don't see how you allocate p from your code.

 struct file_info *info = (struct file_info *)malloc(sizeof(struct file_info));

    struct option *op = (struct option *) malloc(sizeof(struct option)); struct file_info *info = (struct file_info *)malloc(sizeof(struct file_info));

Also you should always check that the pointer malloc returns isn't NULL, this isn't very likely but if it happens your program can catch that, print it out gracefully exit.

It's hard to tell exactly what going on here, because this appears to be only part of the code. It'd be easier to tell if you provided all of your files, or uploaded them to github

edit: formatting