Hi and welcome aboard!
These words are pertinent.
1 John 2:9 (New International Version)
9 Anyone who claims to be in the light but hates his brother is still in the darkness.
1 John 2:11 (New International Version)
11 But whoever hates his brother is in the darkness and walks around in the darkness; he does not know where he is going, because the darkness has blinded him.
1 John 3:14-15 (New International Version)
14 We know that we have passed from death to life, because we love our brothers. Anyone who does not love remains in death. 15 Anyone who hates his brother is a murderer, and you know that no murderer has eternal life in him.
1 John 4:19-21 (New International Version)
19 We love because he first loved us. 20 If anyone says, "I love God," yet hates his brother, he is a liar. For anyone who does not love his brother, whom he has seen, cannot love God, whom he has not seen. 21 And he has given us this command: Whoever loves God must also love his brother.
Obviously, the bible is not gender specific so this applies to sisters.
Clearly, from these verses.
1. They have not cross over from death to life and have no eternal life in them (the Holy Spirit).
2. They are still in the darkness.
3. They are virtual murderers i.e. the root of murder is hate.
4. They do not love God.
5. They are liars.
I suggest you send them the verses and ask them about their relationship with each other.
Hebrews 4:12 (New International Version)
12 For the word of God is living and active. Sharper than any double-edged sword, it penetrates even to dividing soul and spirit, joints and marrow; it judges the thoughts and attitudes of the heart.
All the best,
Stephen