If you are not legally married as of 12/31/16, you MUST file separate tax returns. You would generally file as single, unless one of you provided care in your home for a qualifying dependent that allows that person to file as head of household.
The ex-spouse who pays alimony can take that as a tax deduction. They must include the other spouse's SSN. The spouse who receives alimony must report it as income and pay tax. If they don't, the IRS will come after them since they know how much alimony should be reported from the other spouse's alimony tax deduction.
Don't borrow trouble -- your ex's tax return is not your problem, just do your own business correctly and let the IRS deal with your ex (if it comes to that).
If the home was owned jointly at the time of the sale, each owner will use the "Sale of home" section to report the sale. Each owner would report half the cost, half the selling price, and half the expenses. If the home was ever used for a rental or home office deduction, then each owner reports half the depreciation recapture. Therefore each spouse reports half the gain as taxable income.
If you owned the home for at least 2 years, and lived in the home at least 2 of the past 5 years as your main residence, and never used it for business or a rental, then up to $250,000 of the gain is non-taxable. Unless someone gave you a 1099-S form at the closing, you normally don't even need to report the sale on your tax return when the gain is excludable in this way. If you report the sale in Turbotax and in the end, don't need to report it, Turbotax will tell you so.
