1
The boy who he lives next door is my friend.
The boy who lives next door is my friend.
The teacher who I met her yesterday was very kind.
The teacher who I met yesterday was very kind.
In a relative clause, who already refers to the person. Do not add he, she, him or her for the same person: ‘the boy who lives next door’, ‘the teacher who I met yesterday’.
2
I met a boy who his dad is a doctor.
I met a boy whose dad is a doctor.
Use whose before a noun to talk about a person’s family or something that belongs to them: ‘a boy whose dad is a doctor’. Do not use who followed by his or her here.
3
We all need a person to who we can talk.
We all need a person who we can talk to.
We all need a person to whom we can talk.
In everyday English, we usually put to at the end: ‘a person who we can talk to’. If to comes before the person, use whom, not who. This is much more formal: ‘a person to whom we can talk’.
See WHOM