I think because of your child is living with parent, so his allowance only $315 per month, and his loan portion is $200 per month before September, after Septemeber will be $315 per month.
Allowance :315 x 13 =
minus
Loan: (200 x 3) + (305 x 10) =
Then the answer will be your total bursary.
Hops this can help you, if you still do not understand, you post the calculations here(only the calculations with no name on it), then I explain it to you.
1) 是他现在一但与我分开住,就够条件了呢? No, he must has a new lease with his name, last I heard must be living 60 Km away from parent's house. This part you have to check with AFE.
2) 还是与我分开住需满一定的时间(如半年或一年等)? No fixed time period mentioned in the manual, it depends on AFE's decision.
I do not think is a good idea to try it now, because they will check all your files, including Father, Mother and son. If they do not agree the situation, it will affect all your bursary, I mean for the whole family.