Very occasionally I hear that parents are running with more than one appeal, be it accidentally from the clerk (rare), school (also rare) or the parents either openly or in error (most common).
You know what? I ignore it. I treat every appeal equally, working as if it is the only appeal those parents are making.
Why? Well, I have no way of knowing what evidence is being given to another panel by the parents or by the (other) school, what the other appeals for the other school are or anything else outside the set of appeals I'm hearing. For instance, the school I'm hearing for may have a relatively weak case and the other school a strong one against allowing more pupils (or vice versa). It would be wrong of me to make my decision based on the hopes that another panel may allow it!
If I can vote to allow the appeal, I will, regardless of knowledge of other appeals and regardless of the chance of them winning more than one appeal. If a parent looses the appeal in such circumstances, they might worry that it was because they were appealing for more than one school, but in truth it would be because the other appeals for that school were stronger.