My brothers and sisters are 'in Christ' they are those who are born again and believe God's Word is The Final Authority.
But you are mine.
"Everyone who believes that Jesus is the Christ has been born of God, and everyone who loves the parent loves the child." - 1 John 5:1
"For the one who sanctifies and those who are sanctified all have one Father. For this reason Jesus is not ashamed to call them brothers and sisters," - Hebrews 2:11
Peace and blessings