For twins, if either one gets in the first choice, the other one will automatically be assigned to the the same school. Hence, if you choose the same school as the first choice for both of your twins, your twins' chance of getting first choice would be twice that of other kids.
For example, let's say Twin A and Twin B both choose as 軒灣小 first choice, and as 聖雅閣 second choice, if one of them luckily get in 軒灣小, the other one will automatically be allotted to 軒灣小 as well.
Is my understanding correct?