For all children, if the nearest suitable (not chosen) school is more than 3 miles walk away, the child is entitled to transport or free travel.
I don't think children should be at the same secondary school. I have 2 girls, 1 year apart, and the younger one is always being compared to the older one (older one A* student, younger one is b-c) They are at all girls school. My son goes to all boys school. They all walk to school. My youngest has special needs and the best school for her, was a mixed comp, 3 miles away.
I think you should chose the school for the child, not just plonk a child in a school because siblings are already there.
An 11 year old is quite capable of train/bus/walk to school......it would stop the 4x4 gridlock in the mornings!!!