how does Barsad get information from the Defarges?

He disguises himself, uses a different name, drops many compliments to the Defarges, and spreads a few rumors to get them interested.

Where there rumors?

The rumors had to do with Dr Manette's daughter's marriage in England. The fact that he is Charles Saint Evrémonde, the nephew of their enemy definitely commands their interest.

Okay Honestly I still don't understand:/

Your question was, "how does Barsad get information from the Defarges?" He goes to their place of business and draws them into conversation. Barsad talks about things that might interest them (the Manettes), and he draws them into conversation. Thus, he is able to gain information.