Follow the money. You deduct the share of the real estate tax that you actually paid. You may count the share your husband paid.
If your mother received all the proceeds of the house sale, she is the only one who needs to report it since you didn't get a 1099-S.
If this was her primary residence, and she lived in it 2 out of the last 5 years she does not need to report a gain of less than $250K.
