My father and I co-own a rental property together.
So in reality, you have a partnership.
While the program as well as tax law does allow for "splitting" the ownership of rental property among two or more owners that are not married to each other and filing a joint return, it only allows you to split "EVERYTHING" equally when you report it that way on the personal 1040 tax return. So if you claim 50% ownership you can't claim 100% of the mortgage interest and then say, 50% of the rental income. When it comes to the split on the personal tax return, it's all or nothing.
Your lives will be a whole lot easier if you report the rental income and expenses on a 1065 Partnership return. so that things are reported for and as the partnership you legally have here.