an adoptee, or adopted child
Someone who assaults someone is called an assaulter.
A person holding someone captive is called a captor or kidnapper.
You can adopt someone to be your child but to be your nephew he had to be adopted by your siblings. Then he will be your nephew. There is no nephew-adoption.
A person in their seventies is called a septuagenarian.
This is called a duologue - similar to one person talking being a monologue
The person making the accusation is called the accuser or the plaintiff.
imposter
The law states that the person being adopted must be a child. Therefore, no.
A "Turkish" person
if you mean if someone does not believe in God, this person is called an atheist
It is called suing. You sue someone.
It is called suing. You sue someone.