For some reason, I can't invite more than two sims over on a residential lot, no matter what how big the lot it is, how many sims live on it, etc. Even when I play home businesses, I never have more than two customers on the lot. My laptop has 16GB of ram, an i7 processor, etc, so that's not the problem. Custom content isn't a problem, either, because I've tried removing it and it still occurs. I don't care much about not being able to invite people at parties because I can summon them over but I'm doing a trailer park challenge now and only being able to have two customers on the lot makes it that much harder. Any ideas?

First get BO's unlimited sims mod and add these three lines to your userStartup.cheat:
(you can change all the numbers to what ever you want but the bottom 2 need to add up to the top one.)

uintProp maxTotalSims 50
uintProp maxTotalHumans 35
uintProp maxTotalPets 15

If you don't want 15 pets subtract from it and add to the humans IE: 5 pets and 45 humans.

BO - Unlimited Sims http://www.simbology.com/smf/index....55858#msg155858

the number of guests to a party depends on player's computer. 2 sims is the shipped version number for lowest performance level; highest performance level, 8 sims; medium, I think 5 sims.
the number can be changed through a cheat. intprop maxnumofvisitingsims #
# is the number of sims that could be invited to a party.