1. Who taught Avraham how to do a bris? (18:1)
His friend Mamre. At the end of the Parsha we see that Avraham was very close with Mamre and even considered having Yitzchak marry one of his daughters.
2. Who helped Avraham entertain his guests? What do we learn from that? (18:7)
Yishmael. We see that Avraham sought to involve his son in helping him perform mitzvot in order to teach him.
3. When bargaining for Sodom, why did Avraham not go lower than ten righteous people? (18:32)
Because he knew that less than that was not sufficient to prevent the flood. Noach, his wife, his sons and their wives were eight and the flood still happened.
4. When did the Malachim come to visit Lot in Sodom? How do we know that? (19:3)
Lot fed them Matzot so we learn that it was pesach. It is interesting that the Exodus of Lot happened on the same night that our ancestors left Egypt.
5. What is the meaning of the word 'Eishel'? (21:33)
Eishel means either an orchard or an inn. Either way, it was a method in which Avraham took care of his guests. Some say Eishel is an acronym for achila - food, shtiya - drink, and lina - rest, the three things that Avraham provided.
6. Did Yitzchak know that he was intended to be the sacrifice? (22:6)
According to Rashi at first he did not, but then Avraham either told him or alluded to it and Yitzcha figured it out. Other commentators disagree on this point and say that Yitzchak was unaware.
7. What striking similarity did the descendants of Avraham share with the descendants of his brother Nachor? (22:20)
Nachor had twelve descendants, 8 from a full wife and 4 from a concubine. Yaakov had 12 as well. 8 from full wives and 4 from the maidservant wives.