"Adopt" and adult ...

Hello,

My vampire sim has become a mentor to a very new vampire and their relationship is close enough that I would like them to become siblings, but because they are not from the same family I would like to show in the family three that she "adopted into the family" (kinda like added into the family register kinda thing).

My main vampire has a wife and adopted child, so ideally the "sister to be" would show as aunt to the kid and sister-in-law to the wife 

(if you are looking at the picture, the red head is the new vampire and the blond is the main vampire).

Is this something that is possible?

Thank you in advance

ToKi