Q: My fiancé and his family think we should invite everyone to the wedding with a guest. What's the rule?
A: You needn't invite every single person to your wedding with a guest. In fact, most couples today don't unless they have an unlimited budget. You should, however, include partners of the following people:
Everyone who is married (even if you don't know their spouse)
Couples who are engaged
Couples who are living together
Guests who have had a steady significant other for so long that it would seem awkward not to include their partners.
The last instance is a judgment call, but in most cases your gut will tell you what to do.