ok this may sound compilated but it's not really
1 if your in a game already then open the three dots-option manage worlds then select your household go to the three dots there manage household
2 select your household in the window that pops open another window pops open
3 select the arrows icon click on that another window pops open to select sim to split and merge you'll need to select a houshold in the right panel to move your sim to ( if you don't see a houshold in the right panel click on the tiny down arrow to open the household to select )
4 select the sim you want to move in the left panel then click on the arrow to move him/her to the right panel tick accept and that sim is moved
5 Then select the house you moved your sim to and evict the other sims out but this time select the not in world select the other sims to that panel then close on the x or hit escape button which will be map view and selct your sim you want to play will be in their own home to play withif you wish
thats the way i figured it there may be another way i don't know of yet
if you wish i can take screenshots of the steps if it'll be easier for you to see what to do so just let me know if wish to see screenshots
