Fluffyanimal - Then, I have to say, your district councillor is a twit not well informed about how school admissions work. It is exasperating to hear of people giving out such bad advice that could lead people into real difficulties.
A lot of people believe that if you name only one school, it will show the LEA that that is the school you really, really want your child to attend and they will give you a place accordingly. This is the myth for which your district councillor seems to have fallen.
The reality is that the LEA (or the school if it is its own admission authority) ranks all the applications according to their oversubscription criteria. They work their way down the oversubscription categories until they have filled all their places. There is no additional priority for those who only name one school or for putting a school as first preference. With popular schools, they may not get far (if at all) beyond the in-catchment siblings category, but that depends on the size of the intake, whether there?s a bulge class a couple of years ahead adding to the number of siblings etc etc.
By the sound of it, unless you win the argument about changing the catchment area, your child will be in quite a low priority group for admission to your preferred school. If, as an out-of-catchment sibling, he does not get a place, the LEA will allocate a place at the nearest school which has a vacancy. That may or may not be a school that you would be happy with. There?s a fair chance, though, that the school you?d rather he didn?t go to is one that many parents would rather their child did not go to and so will be the one with vacancies.
So, the fewer schools you name on the application form, the fewer opportunities (it seems to me) you have to influence where your child goes to school. You can still show your preferences by putting your older child?s school first, but as you are far from certain of getting in, you need to decide whether to gamble on where you might be allocated a place if you don?t or to state some preferences for other schools that you would be willing to accept.