What if first child be a boy then will there be only boys. I don't know where you have gathered such information,.
Eventhough certain studies suggest the certain couples with certain blood groups have a chance to have more male babies than the other groups burn it doesn't mean reverse. And as a fact blood groups is not determining factor for sex of the child .it's exclusively the genes . You have 50 percent chance for gettin a boy or girl in each pregnancy
irrespective of the number if pregnancy or blood group . Rest is just by luck or by god .may both favour you .