Madness string 101114

Random mermaid
Kids have a fundamental sense of fairness and when they see a situation where they feel things are unfair, they will sacrifice their own advantage or sacrifice to punish those behaving selfishly in order to maintain fairness. I imagine that you noticed the injustice in the inequality of how your parents treated you both as a child and used your kid logic to correct that injustice to maintain fairness.
If someone's reaction to you setting boundaries or having a differing opinion from their own is to threaten you into submission, whether it's a thinly veiled threat or an overt admission of what they plan to do, this is a red flag of someone who has a high degree of entitlement and has no plans of compromising.