how to give already made sims siblings/parents {solved}

Yes, you need the cas.fulleditmode cheat before entering CAS. I was able to adjust family relations some times, while other times it did not work. So, if you run into trouble, consider saving one sibling to your album, then add to household. All skills/relations will be gone, but I think it might be easier adjusting family relation to a fresh sim. Maybe you did not play all those siblings as much yet.