Darcy is not a one- dimensional person- if he had been like every other person of the higher- circles, he would not have fallen for Lizzy!

]We are not sure of that, I still think that JA implys for Lizzy's thoughts, who is very prejudiced against Darcy .

IMHO, this point of view seems prejudiced by the fact that Lizzy was prejudiced against Darcy!
As we have seen, Lizzy is generally very perceptive(abt the Bingley's, the Colonel, Lady C, etc.).

]We are not sure of that, I still think that JA implys for Lizzy's thoughts.

As others in this thread have pointed out...
Not a syllable had ever reached her of Miss Darcy's meditated elopement. To no creature had it been revealed, where secrecy was possible, except to Elizabeth; and from all Bingley's connections her brother was particularly anxious to conceal it,(Lizzy would never know all this-it is the narrator speaking here) from that very wish which Elizabeth had long ago attributed to him, of their becoming hereafter her own(narrator is saying that Lizzy was right in her conjecture).

] do you think that Darcy will leave his sister " his shy, sheltered sister" marry someone with five sisters ,who are probably have the same manners of Charoline?!!...will not expect to give his sister to anybody beneath his rank.

Bingley is already in Darcy's rank, though he is still clinging to the borders. We are forgetting that though Bingley's fortune was made by trade by his father/grand-father, he is now among the elite. And as soon as he purchases an estate and/or marries well, he will truly be established among the upper-levels.

And as you have pointed out, Darcy loves his sister. He would definitely want her to be married to a kind, and a gentle man like Bingley, rather than a nobleman who might not be!