yes
This will depend on the genotype of the father, but either A negative or O negative.
NO
yes
yes
B negative
no
Yes, it is possible for a mother with A positive blood and a father with O positive blood to have a baby with A negative blood. The baby would inherit one A allele from the mother and one O allele from the father, resulting in A negative blood type.
no
Nothing. Mother and baby will not be harmed because of the differences in blood type.
sometimes
yes
yes