You use who in a relative clause when who is the subject of the clause:
Tom is the boy who works in the library. ( who works in the library is the relative clause and who is the subject of the verb works)
You use whom when there`s already a subject in the relative clause and whom functions as an object (direct or indirect object or object of preposition)
Tom is the boy whom I met in the library. ( I is the subject of the relative clause and whom is the object of met. In this case, whom can be omitted or else you can use who instead of whom )
Tom is the boy whom I was talking to. (Whom is the object of the preposition to. Whom can be omitted or you can use who instead)
Whose is used to show possession.
Tom is the boy whose parents work in the library. (Whose parents = Tom´s parents.)
You use being:
after a preposition: He was punished for being late.
in the passive voice (present or past continuous): A new hospital is/was
In adverb clauses: Being an excellent teacher, Dr. Harper is widely known all
over the world. (Reason)
I hope this helps you. I´m not a native but I´m an English teacher from Argentina.