Depends: https://www.irs.gov/taxtopics/tc505
Qualified mortgage interest includes interest and points you pay on a loan secured by your main home or a second home. Your main home is where you live most of the time, such as a house, cooperative apartment, condominium, mobile home, house trailer, or houseboat. It must have sleeping, cooking, and toilet facilities.
Note that it's interest and points YOU pay on a loan secured by YOUR home.
In order to deduct mortgage interest, the mortgage must be secured by your qualified home and you have an ownership interest in that home. Being the cosigner on the mortgage should qualify as having an ownership interest. A qualified home is either your main or second home. You can only deduct interest and points actually paid by you.
To deduct mortgage interest, you must be either a legal owner (on the deed) or be a beneficial owner, and you must actually pay the mortgage payment. Beneficial ownership is a bit complicated, and I am not 100% sure that only being a co-signed makes you a beneficial owner (but I won't disagree that a co-signer could be a beneficial owner, it's just that it may be more complicated than that.) More importantly, you must be the person who actually pays the interest, or at least part of it, and you can deduct the part you pay.
To deduct property taxes, you must be a legal owner of the property against whom the taxes are assessed, and be the person who pays the taxes. There is no deduction for being a beneficial owner even if you are the person who pays the taxes.