i have had sims living in the same house to get married. they would not sleep together so i had to marry them.
Hmmm.........let me repeat myself. If two sims live in the same house they cannot be married unless you move one out somehow. You can stage weddings..........but that is it, not sure what nookman is talking about.
Yes, you can stage weddings by having them change into formal clothes, and then having them passionately kiss. This way it looks like they just took their vows.
Once I even had some downloads......a sim-looking minister that you buy as a decoration, wedding flowers and a podium.