From the time of your father's death in 1997, you held only a remainderman's interest in the house. That continued throughout the life estate of wife 2. In 2007, upon the death of wife 2, the life estate interest merged with your remainder interest, vesting you with fee simple title. So, your ownership of the house dates to 2007.
Alabama will tax the capital gain, if any, on your 2018 sale of the house, as a non-resident. Georgia will, as your resident state, include this income in your Georgia taxes, as well, but should offer a credit for taxes paid to non-resident states, to ease the burden of double taxation.
The correct order for completion of your tax returns is (1) federal, (2) Alabama, and (3) Georgia.
