rather than changing plans already set in motion, let's look at some options for trimming the guest list:
determine your budget. this not only applies to the funds available to support your event, but also the space available for entertaining.
make lists. each honoree or participant should have a guest list... bride, groom, birthday guy or gal, parents, etc. include every individual you may consider inviting.
strike. start striking names from your own list. as yourself:
how often have i seen this person in the last year?
if i invite this person, will i feel obliged to add other guests? (i.e., additional coworkers, friends)
can i handle the fallout (if there is any) if i do not invite them?
agreement before meeting. before you meet with the others to discuss the lists, determine what categories will be removed entirely - children, co-workers, relationship beyond first cousin, no dates for singles, etc.
meeting of the lists. get together with the other participants, and begin discussing the necessary versus unnecessary guests. if the conversation becomes challenging, then perhaps you can develop a three-strike rule. each person can only strike 3 names from another's list...
the master list. so now that you've removed names from your own list, and the other lists, compile the lists into one master list. if your list still includes too many names, apply the questions provided above in hopes to remove a few more names.
if all else fails, you can always play rock paper scissors!