The Joker is usually depicted as a lone figure without a twin brother. This absence of a twin contributes to his solitary and unpredictable image in the comics.
In certain comic arcs, the Joker indeed has a twin. But this isn't a consistent feature across all Joker-related comics. Sometimes it's introduced for specific plot developments or character dynamics.
It's possible that they have a complementary relationship. If Percy is still the more studious and rule - following type, his twin might be the more adventurous and creative one. They would then balance each other out, with Percy keeping his twin in line when needed and the twin getting Percy to step out of his comfort zone.
No, it is not ethical. Such behavior can cause a great deal of harm to the friendship and family relationships involved. It violates the trust and boundaries within relationships and can lead to emotional distress for all parties.