A neighbor told me that at work he goes to lunch with the same three people everyday. Yet when one of the three was hosting a holiday party, he only invited two of his lunch buddies. My neighbor, who was the one not invited, was offended.
Sometimes we need to remember the basic etiquette rules that many of us learned in kindergarten about inviting classmates to your party. If you invite most of the people in a group, you need to invite everyone from the group. Or, you can invite just one or two people, as long as they don’t make up the majority of the group.
I am often asked a similar question about inviting work friends to your wedding: Do I need to invite my whole department?
My answer is the same. If you invite only one or two close friends, you don’t have to invite the whole department. But if you invite most of the people from your department, you should invite them all. There may, of course, be exceptions. For example, there may be people you rarely see since they work in a different location.
And remember, don’t discuss your event with a group of people, unless all of them have been invited to attend!