Keeping A Family Tree

So I have this family that was the 2 parents, two twin girls, and a son. So long story short, all of the kids aged up, and got married. I moved out everyone except the one girl that was a twin, and her husband. I planned to play on as their life. So then I wanted to move to a custom content world. (Evansdale) I did so, and then once I arrived in Evansdale, I placed my active household's family. (My girl's twin sister and her husband, and her brother and his wife.) I knew that the family tree would get erased, and they would only be able to be friends or whatever, but I was wondering if there was any way to change the relationship between this family instead of being just "friends" to "sister, brother, neice, nephew, sister-in-law" and so on and so forth. I don't have an experiance with mods, but I'd be willing to give them a shot if it meant I could fix the relationships and/or gettingthe family tree back. 

                               Thanks for reading!