to whom had Booker sold Anna the first time - before Comstock existence - and made him stay 20 years in grief and then did the baptism ?? cause I don't get it as he " Booker Dewitt " had sold Anna to the " coming from the future Comstock " the first time , as Comstock hadn't yet existed ??meno_2811

It was never future Comstock. The Booker/Comstock split takes place before the birth of Anna.