In non-defining clauses, "who" is less common as an object, though it is sometimes used in an informal style.
"Whose" is a possessive relative word, used as a determiner before nouns. It replaces his/her/its. "Which" can refer not only to a noun, but also to the whole of a previous clause. In non-defining clauses, quantifying determiners can be used with "of whom", "of which", "of whose". The determiner most often comes before of "which/whom/whose", but can sometimes come after it in a very formal style. Eg: Then the wind spouted in at a ventilating hole-of which there was one on each side…

 "That" is common as a relative pronoun in defining clauses, used irrespective of gender or case except that the genitive must involve postposed "of". It can refer to things, and in an informal style to people. "That" is unusual in non-defining clauses.

 Zero is used often in defining relative clauses. We often leave out object pronouns, especially in an informal style. In non-defining clauses this is not possible.
Eg: Nobody appeared, and he heard the person retreat among the bushes.
Or: Nobody appeared, and he heard the person that retreat among the bushes.
George, the elder, exhibited an ebony-tipped nose…
Or: George, the elder, that exhibited an ebony-tipped nose…

"Who", "which" and "that" can be the subjects of verbs in relative clauses. "Who" refers to people and "which" to things, "that" can refer to both people and thing. Eg:…and other philosophers who follow out a train of reasoning to its logical conclusion..
…and that indifference to fate which is the bases of his sublimity…

"Who", "whom", "which" and "that" can also be used as the objects of verbs in relative clauses. "Who" is informal as an object, in a more formal style, "whom" is used, especially in certain kinds of relative clause.
Eg: He had passed through an ordeal of wretchedness which had given him…
´I shall do one thing in this life, that is, love you, and long for you…´

Defining relative clauses

Defining relative clauses qualify or define a noun and tells us exactly which person or thing are we ta;lomg about.