Similar happened when dd3 went to our local primary (she is now year 6) it is a 15 intake school and there was 14 siblings. All siblings got a space and there was 14 appeals 3 were upheld (C of E school and all 3 regular church goers) At the time the school also operated a unusual pattern over year R 1 and 2 so split year 1 so the keystage 1 was never actually over numbers.
The result has been over the next 6 years the school has changed a few things.
Y1 is no longer split, so it goes 15 in Reception 30 in Year 1& 2 classes. Last year the school send out admission change and as of this september their admission is now LAC children, Children who lives within 4 named parish and regular church goers, Children who lives within 4 named parish not regular church goers, THEN siblings.
There was a uproar over this as the school is popular from a local town (2/3 miles away) however it is really a very fair way of doing it. This way the local children gets in to their local school before children further away gets in.
However it is easy for me to say with 4 children all bar 1 passed through the school. During the consulting stage the school actually said they had only had 1 year where they had more applications from local children than they could take due to siblings (obviously the year dd3 started as they only needed 2 to apply before they were out there)
This year they had 5 appeals and not a single appeal was successful. This has been due to the school changes over the years with the busy sibling year.
DD3 however is most put out that due to people moving schools there will now not be 15 leavers in 2015. ONLY 14.. (they are down to 14 after the initial 18)