Save the Dates, and Invite Confusion

[Deleted User]

We are from Boston, and are planning a destinantion wedding to viva las vegas. In vegas we are doing a rehersal, rehersal dinner, wedding, and then a brunch reception the day after the wedding. When we return home after honeymoon (2 weeks after wedding) we are having a semi-formal reception, where we will  have more of a traditional reception (first dance, tossing the boquet, cake) along with a viewing of the vegas ceremony.

We do not want anyone to feel obligated to come to vegas, so regarding save the dates and invites, what it proper etiquette?