If your parents are inviting 30 friends, don't limit his folks to 20. Your friends who are unattached or unmarried without a long term partner don't automatically require a date. However, if they know almost no one at the wedding, you may allow them a companion. Unless you socialize with your work friends on the weekends, they don't necessarily have to be there. Some exeptions may be your boss or an assistant, with whom you can invite without upsetting other co-workers.
Kids are a lot easier to cut out.
Eliminate all but your neices or nephews or drop everyone under the age of 18. Make sure the rule applies to everyone so that others don't feel left out. It's also polite to let parents know before sending out the invitations. Pick your fights carefully You may think you have won the battle of not inviting your great-aunts, but if it means your Mother is not talking to you, then you've lost the war. If your reception hall has a maximum occupancy of 170, and your guest list is at 195, don't worry.