Yes. A child of theirs can either be B negative or A negative.
yes, the mother could o negative
This doesn't say much about the father - he can have any blood type, except AB. He can also be either Rh positive or negative.
no
yes
Yes, a father with A negative blood can have a child with A positive blood. If he does, the mother must have a positive Rh factor, and the mother's blood type may be any of the possibilities.
more than 99% not.
I'm not sure how negative or positive is determined, but a B mother and O father can have a B child.
yes.
No
a-
A or AB
B negative