Sims 2 Legacy: Sims Disappearing and being replaced.

I started with a family of four: two parents, one teen and one baby. I attempted to move my teen to college and realised I hadn’t created the college world yet so saved the home and created the college worlds however when returning to the home, my teen and baby had disappeared and a random new sim had moved into the property with the parents. I went out and checked the loading screen which still had my teen and baby but every time I went back into the property those two were no where to be found and the random was there. I checked all the college bins just in case and am bamboozled by what happened!