I don't know if you mean royal events on a grander scale (where members of several royal families are invited) or royal events within a royal family, do remember that in most cases there are a limited number of seats/how many people can be invited unless it's an outdoor event.
Take for example the wedding of crown princess Victoria, invitations were sent to all the royal families in Europe, Middle East and Asia but we don't know how many persons from each family was invited. I would guess when it comes to members of the Bernadotte family (the king's sisters with families, aunts, cousins etc) most of the family membes were invited, as well as the members of the Danish and Norwegian royal families, and also the Dutch royal family got several invitations due to their close connections to the Swedish royal family, while royal families that are not as closely related to/friends with the Swedish royal family the invitations was only to the head of the family and/or crown prince with spouse. Even if you are a royal you have to get an invitation to an event, you can't just turn up and expect to be welcomed as a guest.