Instructions
Start the PC game, choose a neighborhood and choose a house with a couple.
Buy a two-person bed, if there is not one in the house. To buy a bed, click on "Buy Mode." In the tab, click the "Chair" icon, then click the "Bed" icon. Scroll through the beds and click the one you want. Move your mouse to the desired location. Use the "Period" and "Comma" keys to rotate the bed, if necessary. Click to release the bed. Click "Live Mode."
Select the bed. In the menu, select "Relax." Repeat this process for the other Sim. Both Sims should be in the bed.
Click on the Sim you are not currently playing. Click "Try For Baby" in the pop-up menu. If the female Sim is pregnant, a short music clip will play at the end of the animation. If the music does not play, repeat this process.
Press "Ctrl-Shift-C" at the same time to bring up the "Console" window. Type "ForceTwins" and press "Enter." Pregnancy lasts three Sim days, according to the Pregnancy Guide.