To qualify as tefilah b’tzibur, must all ten participants in a minyan be davening?

Tefilah b’tzibur is when a person davens Shemoneh Esrei together with a minyan of ten men. According to some Achronim, at least ten people must be davening at that time. It is not sufficient to have a situation where most of the ten people are davening but a few non-daveners are there to complete the minyan. Although generally in halacha we employ the rule of rubo k’kulo (a majority has the same status as the whole), this opinion holds that tefilah b’tzibur requires davening with the entire group. Other Achronim do not make this distinction and hold that under pressing circumstances, one may daven with a tzibur that only has six people davening. Some are of the opinion that one may be lenient for Shacharis and Mincha, where the obligation of Chazoras Hashatz binds all ten people together. During Ma’ariv, however, when there is no Chazoras Hashatz, the tzibur only has a connection if they are all davening.

ס"ק ח; ביאורים ומוספים דרשו, 8

How can a person who missed the minyan still hear Kaddish and Borchu?

There is a concept known as pores al Shema. This means that if there are people who did not hear Kaddish, Borchu and Kedusha with the tzibur, they may organize a minyan, appoint a chazan to say Kaddish, Borchu and the brocha of Yotzer Hameoros out loud, immediately followed by the first three brochos of Shemoneh Esrei and Kedusha. L’chatchila, this should only be done if there are six people who have not yet heard Kaddish and Borchu. If six people are not available, one may be pores al Shema even for one person who has not heard the devarim shebekedusha. According to the Rema, it is not necessary to say Yotzer Hameoros out loud, and if the chazan began Shemoneh Esrei he should complete all the brochos. Shulchon Aruch and Rema both agree that one may be pores al Shema even if all the people in the minyan already davened (on their own). Others hold that there must be at least one person who has not yet davened.

ס"ק ח; ביאורים ומוספים דרשו, 8 וראה ביה"ל ד"ה אומר

Why should Borchu be said at the end of davening?

There is a minhag to repeat Borchu at the end of davening for those who came late. Some congregations say it after Shemoneh Esrei and others say it after the final Kaddish. The minhag is to say Borchu even if everyone came to shul on time. Some shuls do not say Borchu on days when there is Kriyas HaTorah, since it is highly unlikely that the latecomers did not hear Borchu during Kriyas HaTorah.

הקדמת המשנ"ב לסימן סט וס"ק ט-י; ביאורים ומוספים דרשו, 1

• When saying a brocha, one may not diverge from the text that Chazal composed. In the literature of Chazal, however, we find that they wrote only the beginnings and ends of brochos and determined whether the brochos would be long or short. Regarding the middle of brochos, however, we do not find exact texts from Chazal. Therefore, if one omitted or changed the nusach that is found in the siddur for the middle of the brocha, he is yotzei the brocha bedieved if he mentioned the primary concept of the brocha.

• As the generations progressed, various nuschos hatefilah developed. According to the teachings of Kabbalah, there are twelve gates of tefilah in Shamayim, corresponding to the twelve shevatim. The Ashkenazic and Sephardic communities each have their own nusach. The Sephardic one is known as Edot Hamizrach. Ashkenazim and Sephardim also have different pronunciations of Lashon Kodesh. The poskim are critical of Ashkenazim who adopt the pronunciation of Sephardim.

• There are various opinions among the poskim as to how a person should conduct himself when he davens in a shul which does not follow his nusach. 

• Forming a personal minyan in shul

• When would a person say Borchu before davening?

• Can a second minyan start when people from the first minyan are still in shul?