1) How was Avraham's brit done in detail, because it was so hard to do it this way? 2) What's the difference between Jews' brit and the Arabs' brit?

We don't have details how he did it, but assume that it's similar to the traditional circumcision which was done from his time until today! The Arabs don't do "priya" to cut and fold over the thin membrane beneath the foreskin called the "inner preputial epithelium", to reveal the organ itself.