@Sarah515 I agree with @Opus 17 especially if you considers your dad to be a 50% owner. My only thought on this is that what was your dad's intent for the down payment? Does he think he's a 50% owner as well? If not, could his down payment be a gift. Was his share of the down payment below the annual exclusion amount? Did he file a gift tax return?
If your dad considers himself a 50% owner, then I would think he should pay for half of the mortgage payments and maintenance costs.
Since you're paying 100% of the mortgages and maintenance costs, I would think you should be able to deduct 100% of the mortgage interests and maintenance costs. On depreciation, may be you should only enter half of purchase price + closing costs (less land portion) as basis into TT in year one since you only owe half of the property. Your ownership percentage would increase each year by the principal repayment since that's the only amount not deducted on Schedule E.
