Hi,
In order to get tax benefits on the home loan obtained by you, it is no where stated that you need to be the owner of the house property.
Rather, what is important is that you should be the "CO-BORROWER" or "CO-APPLICANT" of the said home loan. Even a Guarantor or mere repayment of home loan from your income is not sufficient.
If you want to refer the section, go through Section 24, which says "Borrower" and "Borrowed Capital".
Hence, in order to be eligible u/s 24, you should borrow the money as home loan, which is possible when you are co-borrower or co-applicant.
As such, if in the said home loan you are regarded as co-borrower, you will be eligible to claim deduction u/s 24.
Further, since you occupy the house along with your mother, as per Sec. 27(iiia) read with Section 53A of Transfer of Property Act, you will be deemed to be the owner of that house.
Secondly, as far as 50-50 share with your aunt is concerned, you will be in any case eligible to claim your proportionate share of tax benefits, irrespective of the fact whether your aunt claims it or not.
I hope it is clear to you now.
Regards,