Ask Colin: Etiquette
Our son and his fiancé are getting married on a cruise ship. As such, they are limited on the number of attendees, however, I told them there are some folks that "need" to be invited simply because of our relationship with them and I am quite certain they will not attend, but be offended if they didn't get an invite and send a gift. My son is reluctant to do this as he has a fear they will all say yes and then they will be in a bind!
In an instance like this, it would serve both sides if you did the following: Send an announcement to all out of town guests and an invitation to all invited guests. If they are not coming, they are not obliged to send a gift.