Maran rules in Siman 8 that if three or four people are putting on their Tallit, one person may recite the Beracha "L’Hitatef B’Sisit" on behalf of everyone, provided he has them in mind, and they listen with intent to fulfil their obligation. Moreover, the Mishna Berura (Rav Yisrael Meir Kagan of Radin, 1839-1933) comments that not only is this permitted, but, it is actually preferable, because of the principle "B’rov Am Hadrat Melech" (There is more glory to the King, when Misvot are performed in a larger gathering).
Moreover, the Mishna Berura says an even greater Chidush (novel Halacha): Even if a person has already donned his Tallit and recited the Beracha, he is allowed to recite the Beracha again for someone else to fulfil their obligation. That is, if someone else wants to put on a Tallit, even if he knows how to recite the Beracha, the first person can recite the Beracha on his behalf. This is based on the principle of "Kol Yisrael Arevim Zeh L’Zeh"-All Jews have a mutual responsibility to each other. When we received the Torah at Mt. Sinai, not only did we accept its obligations upon ourselves, but we also accepted responsibility that all other Jews perform the Misvot. Therefore, even though one had already fulfilled the misva of Sisit personally, he can recite the Beracha again for someone else who has not yet fulfilled his obligation. Another example is Kiddush. Even though someone has already recited Kiddush on Shabbat, he can say it again and again for other people who have not yet performed the Misva.
Rabbi Shelomo Zalman Aeurbach points out that applying this principle to Sisit is a Chidush (novelty). As opposed to Kiddush, Sisit is not an absolute obligation, as one who does not wear a four-cornered garment does not have to attach the Sisit fringes. Nevertheless, the principle of "Arvut" (mutual responsibility) applies.
While this is true in principle, the accepted custom is for everyone to make the Beracha on the Tallit individually, and not rely on someone else’s Beracha. The reason is that it is hard for people to precisely synchronize putting on their Tallitot together. Also, many people are not familiar with the proper procedure for listening and intending to fulfil their obligation through someone else. Of course, with regard to the Beracha on Hallel and Kiddush, the accepted practice is for the Hazzan to recite the Beracha on behalf of everyone. Anyone separating himself from the group and reciting it by himself is performing the Misva in a non-ideal way. This is also the accepted custom with regard to eating the Karpas on the Seder night. The leader should recite the Beracha of "Boreh Peri Ha’Adamah" on behalf of everyone. This preferable to making a "Beracha Party," in which everyone says a Beracha in order to answer Amen to each other’s Beracha.
In cases where the Hazzan recites the Beracha on behalf of everyone, a person has fulfilled his obligation by listening to the Beracha with intent to be included, even if he does not say "Amen" after the Beracha. This is the ruling of the Mishna Berura, to which Hacham Ovadia concurs.
The custom is for everyone to make their own Beracha upon donning their Tallit.
Everyone should fulfil their obligation to recite the Beracha of Kiddush, Karpas and Hallel with the Hazzan.
If one listened to the Beracha of the Hazzan with intent to be included but did not answer Amen, he has fulfilled his obligation.