In the other lessons, i saw that "De qui" "Qui" "Dont" "Lequel" and "Duquel" are having the same literal meanings in the English translation. Can, you explain this briefly?
Eg. Le garçon à côté de qui tu es assise a de beaux yeux.
Eg. Voici les amis au sujet desquels nous sommes inquiets.
Eg. Le garçon dont tu parles est très gentil.
Eg. La fille derrière qui je suis assis est belle.
All of them means "Whom' may i know why? and all of them seem so complicated while they literally mean the same.