Question

IF A DIZYGOTIC TWIN HAS A couple with heterozygous b blood group

Answer 1

HERE IS YOUR ANSWER!

There is a 75% (3 of 4) chance that the child will be Type B, and a 25% (1 of 4) chance that the child will inherit Type O (ii)

Yes definitely if they are fraternal twins and, although much less common, it is also even possible if they are identical twins.  In fact mom, dad and twins could all end up with different blood types!

Fraternal twins really aren’t any different than two siblings (except they happened to share the same womb at the same time).  Each of these twins is the result of a separate egg being fertilized by a separate sperm.  So whatever is true for brothers and sisters, is true for fraternal twins too.  And since brothers and sisters can have different blood types, so too can fraternal twins.