When you sell someone else's product, it is called "reselling" or "retailing."
Someone who picks on someone else is called a bully. They are not nice people.
When someone else writes about someone who is deceased, it is called a biography.
Copying someone else's work without permission is called plagiarism.
Envious.
AutoBiography
• Someone who interferes in someone else's life is called a 'meddler.' Obviously.....
The term for someone who does this specifically is "two-faced"
a babysitter
"Somesle" is not an English word. Perhaps you mean "someone else" or "something else"?
Tenant
imposter