Does anyone know what makes bipolar and schizophrenia different since both are 2 personalities?

No: There are probably multiple reasons why some folks are bipolar and others are schizophrenic. Most likely there are multiple genes involved in the difference, there may also be environmental factors (experiences of growing up) that are associated with the two disorders.

They aren't: Schizophrenia is a brain disease involving one's thoughts and is associated with psychosis. It has nothing to do with two personalities. Neither does bipolar disorder, which is a mood disorder. Many think there is some kind of split personalies, but that is just not the case.