A murderer or perhaps a Kinslayer.
The term you are probably looking for is "fratricide"
Regicide
a murderer.
She will be referred to as the sister of someone's brother-in-law.
carer
Your brother or sister.
a butcher
Your brother's wife would think of you as her brother-in-law and when wanting to get your attention will simply call you by your first name. If she is introducing you to someone she would say, 'This is my brother-in-law ____.'
If person married to your brother is a woman? She is your Sister-in-Law.
Brother Joe might be someone who is a fellow christian in a church or it could be Brother Joe from the Elks Lodge or the Masons or other organizations where they recognize each other as "brother" because of their closeness.
A person who kills plants is generally referred to as a "plant killer" or someone with a "black thumb."
Fratricide is the killing of ones brother or sister So you would call him a( Murderer )
civil war, brother kills brother.