In terms of poitics, King Hamlet's murder and King Claudius' subsequent marriage and taking the crown is the only part of the plot that directly pertains to the subject. Familial problems, however, serve as the basis for the plot. Take away the crown, and Claudius is still responsible for his brother's death.... he has still married his brother's wife, and Hamlet will still seek revenge based upon those facts. Would Claudius have killed his brother regardless? Would he have married Gertrude..... was she a part of the plot?
These are the things we will never know, as Shakespeare wrote this play to depict the politics, as well as the family dissention. They are not separate issues.