Hey guys! I created a family and forgot to edit their relationships. I searched for the solutions here and kind of merged some solutions and my problem was solved. I just saved the game after moving my family into an apartment then i selected "exit to main menu" option from the top right corner of the screen and when I reached the main menu I selected the option of "Create a family" and after I got there I created sim of my choice which I could merge with my existing family for example, I created a boy, because I already had a little girl in my family and she was an only child and now she had a brother. and then I selected "Family Library" option from the top Right corner of the screen. and selected my existing family and then selected move this family from the window that opened once I selected my family, and selected "merge". Then i edited their relationships and got them a house. and deleted my previous family from the family library which did not have the boy. And rushed here and registered and wrote this comment. My game window is still open. I am gonna go there now and play my game.
Hope it helps.
PS; I did this in Sims 4