Pre-Made's Offspring

I tried for a long time to have one of my Sims flirt with Bella Goth, but I managed it eventually. It became a challenge for me. My Sim would rock up at their house as often as possible but most of the time her brother would rant and rave if any flirting took place. After weeks of careful progress I was amazed when the woohoo option appeared, and so they went for it. However, as soon as they went to bed the family appeared from nowhere and stood in the bedroom ranting. A dialogue box came up saying this activity was inappropriate and the software forced my Sim out of bed to be shouted at. Every time I tried it again and threw drinks at the family. Eventually the deed was done, but then my Sim floated up to the ceiling and into the floor above (which actually does not exist at that house). It was a big penthouse type of room with large windows all around the walls that I could see, and men sitting in front of rows of computers. I thought it was interesting and would have a look around but as soon as I tried to move the Sim, the room vanished, the screen went white for a second and he found himself outside in the middle of the road. I am not drunk, nor am I making this up. It only happened that once and I have never been able to do it again, despite getting my Sim to elope with Bella and live in the Goths' house for a while.