Sims 4 father

In the sims 4 if you give a character father winter’s child trait it basically in a way can not be removed. I removed the trait from one of my sims so that I could make his sister his full sister cuz it says half. To do this I was going to create their father to connect them together. So I removed the father winter’s child trait from the male sim and went into edit house hold to make them a dad after it was removed. You can not make the sim the father of the one who had the trait even though it is gone. It just won’t let you. It did let me for the female sim who did not have the trait but would not for the male who originally did. I tried several thing’s to fix this. I do not want to remove the sim from the world and upload him again into the world(Which did fix him not having a father when I tried that as I could give him one) because it will destroy his relationships with other sims already in the world which I can not fix such as his kids.. it tells me I can’t change the relationship of pre-existing sims. So for that reason I can’t go that route. I am an Xbox series X player so I do not use mods or anything other than the basic cheats such as add or remove traits such as discussed here. This issue being fixed would be helpful! I’d like to make him and her full blood brother and sister. Thank you!