It is not at all irrational. In fact it is completely rational when you think about it. Same school, same families and possibly some of the same teachers.
Your most recent post though makes me feel that there is more to this which you need to pick about a bit.
Children can be awful to each other. So can adults. Being unkind and trying to put yourself at the top of a pecking order is part of human nature which leaves a lot to be desired.
Conflict will happen at any school your children attend. No school can claim to be conflict free. The very best pastoral support teachers cannot protect a child from experiencing conflict or unkindness. Therefore the only thing you can really hope happens is that your children are resilient and full of self-confidence which helps them bounce back.
Bullying can be awful and insidious and a good school should have policies for managing that. Those policies will be different to how they manage normal conflict however. But still, part of the process is on supporting the person who has been targeted and building their coping mechanism.
Does any of that make sense?
Is the school good in other ways? What about your options?
Lots and lots of kids go to schools which are not in their area. They cope fine.