Again, you say "gifted" above. That has a specific meaning. "Inherited" has a different meaning.
She could have placed you on the deed making you co-owners (1/3 share each) and you inherited her share only when she died. Or she could have gifted you and your brother 1/2 each while she was alive, so you were the only owners (but this causes trouble with the reverse mortgage so it probably was not this.) Or she could have gifted you the home with a life estate (which may or may not cause problems with the reverse mortgage.
You may need to check with the lawyer who handled the estate.
Assuming you mean the home was inherited, and you did not have any form of title until after she died, then the answer above applies. Your "gain" or "loss" has nothing to do with the amount of the reverse mortgage, or who got paid what amounts when the home was sold, or how much cash you actually received. Gain or loss only involves the selling price and the cost basis.
Your adjusted cost basis is the fair market value, plus any improvements you made after inheriting the house. Repairs are not improvements. Repairs restore a property to as-was condition while improvements add value or extend the useful life of the property. A new tear-off roof is an improvement. Patching leaks so you can sell is a repair.
For example, let's say you inherited the home on June 1, 2016 and sold it on September 30. That's close enough that you can use the selling price as the fair market value on the date of her death. The selling price was $120,000 and the real estate commission was $8,000. Therefore the amount realized from the sale was $112,000. You can't take any adjustment for repairs. If the fair market value on the day she died was $120,000 and the amount realized is $112,000, then you have a $8,000 loss. Each of you reports have the value, half the selling price, half the commission, and takes half the loss. It doesn't matter how much was paid to the bank to pay off the mortgage or how much cash you actually received.
On the other hand, let's say the roof work qualifies as an improvement -- like a whole new roof that will last 20 years for the next owner. Then, your cost basis is $120,000 fair market value plus $5400 roof = $125400. Your selling price is $120,000, your commission is $8000, so you have a loss of $13,400. (divided in half for each of you).
In Turbotax, do not report this as "sale of a home". Instead, report it as sale of an asset under "Stocks Bonds and other Assets" on the Income page.
If you paid "pre-taxes" that sounds like you are in a state where property taxes are paid in arrears. Those are not adjustments to the selling price, those are property taxes, and they are deductible in the property tax section and are not an adjustment to the asset sale.
Turbotax can handle the sale of an asset just fine, but you have to know the rules about fair market value, the difference between adjusted cost basis, what expenses are adjustments to basis and what closing costs are tax deductions and what closing costs are not deductible at all. Turbotax does not hold your hand though every little detail, you have to have some knowledge. So in the sense that a CPA is better, what do you expect him to say? You can pay him $300 to hold your hand and explain everything, or you can use turbotax for $80 and then you have to know more of the tax details on your own.
From your explanation above, either your CPA doesn't know what he is doing, or you are confused (or lacking knowledge) and he is withholding facts to convince you to pay him. (The mortgage payoff has nothing to do with gain or loss and you can't take a tax deduction for the mortgage payoff. The property taxes are deducted differently and other closing costs may or may not be adjustments to the purchase price for the gain or loss calculation.)