From your E-Mail, you mother is not fully and/or completely dependent only on you, because you have brothers supporting her also.
My advice:
Withdraw her from your application to DIAC, simply because not to get a refuse of your application as primary applicant.
Once you are in Australia, you can sponsor your mother without taking chances or risks.
Me. Fadel Fawzi, LL.B, M.C.L., LL.M, Ph.D
Int'L & Immigration Lawyer, Juridical Counsellor,
CBA #8204060 /IBA # 1018179 / Ontario Bar Association
Head Office:
Immigration Services
Web.
http://icuimmigration.comTel: 1-514-333 6365 Canada
Tel: +202-33459623 Egypt
+20-163309269 Egypt
Tel: +982-1-88910752 Iran
Tel: +61 0422111447 Australia