Anyone good at science? Blooding typing and genetics?

through ysis of a pedigree chart we can conclude that granny's genotype would be AB for blood type the reason for this is because the blood type O is recessive to all other types, since there first child has children who are both blood type B we can conclude that there first childs blood type too should B and for there second child the blood type is A which was given to us, therefore saying that grandpa and granny's children have blood type B and A. therefore we can conclude that since there is a mixture of blood types in the second generation we can conclude that granny's blood type should be AB.