What is proper wedding gift notification etiquette for family or friends?

We had a destination wedding in Key West three months ago. We invited a large amount of family to the wedding, but a majority regrettably declined. Within the wedding invitations were detailed inserts of where everyone can purchase wedding registry items for us and where they can be mailed. My own siblings still have yet to purchase gifts for us! Is it inappropriate for me to ask, or is it not required they provide a gift if they did not attend the wedding? Is there a standard “waiting period” that grants invited family and friends forgiveness before I should be really concerned, or are we being completely selfish? Please help me calm my frustrations, fellow Jellies!