I hope I am misunderstanding but are you trying to imply that it's okay to love your siblings less and treat them as a nuisance if they don't share genes with you?
Even if I looked at this situation from an entirely self-absorbed perspective and put morals aside, wouldn't it make more sense to love a half-sibling less than an adopted sibling? Since a half-sibling sibling has other family that is not yours but with an adopted sibling you share everything in common just like you do with a full genetic sibling.
Also, you are more likely to have been completely raised alongside your adopted sibling unlike in the case of a half-sibling where you're either living completely seperate lives or are at least cognizant of the fact that you have different, often competing allegiances.
Since kin identification in social animals like humans is based on recognising fellows that you were raised with as your kin, technically an adopted sibling is likely more of a sibling to you, similar to a full genetic sibling, than a half-sibling is. I am not being accusatory yet. I just didn't understand what you were trying to get at by bringing up the fact that the younger sister wasn't genetically related in response to a comment talking about a character who commits fratricide.
How can you be a first born and be thinking of killing your own lil sister,it doesn't matter if you don't share a mother.ssshm petty grown ass man.get your rugged ass down.am done venting,and if it was not you whom did it sorry