@Arielle08 - There is a mod where you can have up to 24? sims in one household...but I put them in separate households. It's much easier to manage.
@MacNcheese123 - You can't really. They may have patched it? but only a certain number of sims will turn up in the invite section when you go to throw a party. With the new groupings they introduced with Get Together sims will generally stick together and do the same things. The way I've worked around it is to just assume that the girls who don't turn up in the invitation window are considered safe.