Here, you can add or remove relationships (parents are not included because I couldn’t get the family tree to update the way MCC grandparents and siblings worked). To use the mod, click on the desired sim and click on the Set Family Relationships Menu. This mod allows you to add those relationships! I use it to add cousins since the game only recognizes first cousins in the relationship panel by default. However, you cannot add cousins, uncles, aunts, grandchildren or grandparents yet.
It allows you to add siblings and parents to desired sims.
One of the features I love about MC Command Center is the ability to add relationships.