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.com

Tel: 1-514-333 6365 Canada
Tel: +202-33459623 Egypt
+20-163309269 Egypt
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Tel: +61 0422111447 Australia