yes, you can have them as sponsor. They will just submit an Affidavit of support that they will be providing financial support (notarized by Justice of the Peace/Notary Public) stating:
relation of sponsor to student ;if non-relative:
state how the sponsor knows the student and how long they have known each other)
that the sponsor will provide financial support for expenses (i.e. tuition, living & travel costs) incurred by the student while he/she is studying in Australia.
that the sponsor will grant the student access to the funds intended for his/her expenses.
4.contact details of sponsor (i.e. address and phone numbers).
how the sponsor is being compensated or repaid (if applicable).
reason why the sponsor is willing to provide financial support to the student.
Note: All sponsors included in joint bank account/s must sign an Affidavit of Support.
They must also provide their financial docs.