Regarding the laws of Brit Milah. Maran in Yore Dea, siman 265:6, writes [listen to audio clip for the exact quote] that one should preferably try to have ten men present at the Brit Milah, as a Brit Milah is an occasion that should have a Minyan.
One of the reasons brought down is that the purpose of having a Minyan present is to show thanks to Hashem in front of people that the baby came out alive. A baby coming out of the canal is like a person that is freed from prison. When one gets out of prison he has to make Birkat HaGomel. Since the child can’t make Birkat HaGomel for himself, his father makes a thank you to Hashem on his behalf. In the Berachot recited during a Brit Milah is the prayer ‘Hodu LaHashem KiTov, Ki LeOlam Hasdo’ which is prayer thanking Hashem. This way the father is thanking Hashem on behalf of his child. Additionally, the Rabbi makes the Beracha of Bore Peri HaGefen, and gives the child wine to drink, because it is really his Mitzvah as well. Therefore, the Milah should preferably be done with 10 men present.
It should also be pointed out the Taz (Rabbeinu David HaLevi 1586-1667) in Yore Dea, siman 264, seif kattan 9, brings down that if there are other Mohelim present at the Milah, they should be watching everything that is taking place during the actual procedure. One might think they are being nosy, but the Taz holds that it is better to have more Mohelim watching the Milah. He says that sometimes when the Mohel uncovers the foreskin, sometimes it rides back up and covers, and there is a risk that the Milah is unkosher. When there are other Mohelim watching, they can refute any claims that the Milah was not Kosher because they were watching closely. Therefore if there are other Mohelim at the Milah, they should be close up to the front so they can watch and be witness to the Milah, should any question arise later about the Kashrut of the Milah.
