The Punnett square shows that 50% of their children will have the AO genotype and 50% will have the BO genotype. Neither of these genotypes give the child type O blood, so it is impossible for the child to have type O blood. The child would need two O alleles.
I'm pretty sure 2 and 4 occur before cell division and 3 doesn't. I'm iffy about 1 but I'm leaning towards yes. I hope I helped and didn't just sabotage you.