There are a couple of epistles that say you should love them. The book of Hebrews says to keep loving one another as brothers and sisters. (Maybe that’s not actually about actual siblings, but it still only makes sense if you should love your actual siblings.)

1 John says has quite a bit to say in favor of loving your siblings. It says if you love your brother or sister, you live in the light, and there’s nothing in you that will make you stumble. But if you hate your brother or sister, you’re walking blindly in the darkness. It says God has commanded that we must love our brothers and sisters. If people don’t love their siblings, you know they’re liars, murderers, and children of the devil, who don’t love God and will not have eternal life.

Jesus himself says just being angry with your brother or sister will bring God’s judgment on you. He seems to think God takes grudges between siblings more seriously than things that God actually made laws about.

But Jesus also says people who don’t hate their brothers and sisters can’t be his disciples. And Paul says the debt to love one another is a debt that should remain outstanding. In other words, don’t love anyone.