you are not renting at FMV. if taxes are $14,000 a year but rent is only $13,200 there is something different about your property than others in the area. The $13,200 does even include other out of pocket items like repairs, mortgage payments, etc. $it seems $1,100 is room rental rather than house rental which is what you mon is doing. the IRS does not allow you to take a rental loss on property rented to relatives at less than FMV
you may want to reconsider purchasing. your only deductions would be real estate taxes and mortgage interest on schedule A. if your taxes such as state income taxes and real estate taxes on your own home already exceed $10,000 you will not get any further benefit from the real estate taxes you pay on mom's house. if your mortgage on your own house is close to $750,000 or maybe a $1,000,000 the deductibility of the interest on mom's house could be limited.
