This is really easy but you will need a expansion pack(Sims Hot-Date) on your The Sims: Unleashed, the people who are about to get married has to be a different family the man sould go to town(not old town) and buy teddy bear, Red flowers, chocolates and diamond ring.
Give the gifts from man to women(make sure the women or the person who will receive the gift is happy)then choose a kiss opstion dont use a very good one like ''Fiery Kiss''
then keep the relation going good when the friendship meter goes to friend and red heart after that it will give you a opstion to prupose then they will immediatly change to their formal cloths then kiss then the picture will go on to your album and your Done!!