That's an easy one supposing your ok with cheats?
Type in the cheat bar testingcheatsenabled true now go to your sims relationships box and pull up the green in the bar till its full
now they are besties it will be much easy it is even easier if you have a sim with the romantic trait that way they can flirt and that leads to kissing
if you don't have that trait don't worry you can press and hold control and click on the sim and change the traits (that only works if its your sim) and you must have the cheat on to do that
Chat with our AI personalities
If your sims are already best friends, flirt with or kiss them. If not, get them best friends while flirting/kissing them
ewww and no, not unless their related by marriage. But you can make sims have the same last name even if they aren't made at the same time. Then you can have a Mr. Smith already in the neighborhood and create a Miss Smith. Move them in together and have them fall in love.
In the Sims series of games, your Sims won't want to fall in love until they know each other well... so you have to get your sims to have conversations with each other, and know each other really well, and that will open up additional "love" options, like giving them a hug. :) If you take it slow and don't try to push them into it too fast, you can usually get any two sims to fall in love with each other.
You keep romancing them. if you do it enough they will become your soul mate!:) You keep romancing them. if you do it enough they will become your soul mate!:)
You make your sims best friends,