Increasing in blessings for many individuals – May a person doing a Mitzvah multiple times in one session honor several individuals to do so with a blessing each time?^[1]

No. Only a single blessing may be said on behalf of all the people.[2]

Bedikas Chametz:[3] A homeowner may appoint another person to help him perform the Bedika of his home together with him when he searches. The emissaries are not to say their own blessing prior to beginning to search and the blessing is to be said only by the homeowner. This applies even if they were not present when the homeowner said his blessing^[4]

Mezuzos:[5] If one desires to honor several people to put up the Mezuzos in his property, then only a single blessing may be said on behalf of all the people putting up the Mezuzos of a single property.

Hafrashas Challah: If one desires to honor several people to separate Challah from different batches of dough that contain Shiur Challah, then only a single blessing may be said on behalf of all the people separating the dough of a single owner.[6] However, if there is a clear Minhag of women to permit all the women to say a blessing, then they may each say a blessing.[7]

Hadlakas Neiros Shabbos:[8] Some Poskim[9] rule that all the people who light candles within a single home may only say one blessing, having the mother of the home say the blessing on behalf of them all. Other Poskim[10], however, rule that every individual may recite the blessing when they light the candles in their area.[11] Practically, the Ashkenazi custom is like this opinion.[12]

Shofar:[13] One may have another person substitute him in middle of a set if he is unable to complete the blows, however the substitute is not to repeat the blessing prior to blowing as he has already fulfilled his obligation with the blessing said by the first blower.

Bris Mila:^[14] Upon circumcising twins simultaneously, a single blessing is to be recited on behalf of both children.

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[1] Admur 213:7 in parentheses “When a number of people are fulfilling a single complete mitzvah on behalf of one person, of which the entire mitzvah is upon his shoulders to fulfill, then they may not split up and each individually recite a blessing over their performance of one part of the mitzvah. Rather, they all must be together during the blessing in order so one of them says the blessing on behalf of them all.” [see also Admur 263:15; Kuntrus Achron 263:2; 432:9; 457:4; 585:9; Shut Tzemach Tzedek 116; Ohalei Sheim 7:103;  Koveitz Hearos Ubiurim 798 p. 85]; Michaber O.C. 432:2; Y.D. 265:5; Tur 265; Shut Harosh 64 in name of Rabbeinu Simcha; Chok Yaakov 432:11; Olas Shabbos 432; Elya Zuta 585; Shulchan Gavoa 289:4; Sova Semachos 4; Rav Poalim Y.D. 2:2; Yechaveh Daas 2:32;  Chayeh Halevi 1:94; Shaareiy Mezuzah p. 377; See Sefer Sechel Tov 289:48; Piskeiy Teshuvos 213:2

Other opinions: Some Poskim rule that every individual may recite the blessing when they do their part of the Mitzvah as they are all obligated in the Mitzvah due to Din Areivus. [2^nd opinion in Admur 263:15; Kuntrus Achron 263:2] Practically, Safek Brachos Lihakel, and hence one may only rely on this opinion in a case of a clear Minhag, such as Hadlakas Neiros in different rooms of home, however, not by Bedikas Chametz or Shofar. [Kuntrus Achron ibid] Liekwise, by Hafrshas Challah the custom is to be lenient. [Admur 457:4]

[2] The reason: Since one does not fulfill his obligation of this mitzvah until all of them fulfill their part, it is considered that the mitzvah is not complete until all of them perform their part, and therefore it suffices for one blessing to be said and it is forbidden to cause an unnecessary blessing to be said. [Admur ibid in parentheses]

[3] Admur 432:8-9

[4] Admur 432:9; Kuntrus Achron 263:2; Chok Yaakov 432:11; Olas Shabbos; Elya Zuta 585

The reason: The reason for this is because the emissaries are not obligated in doing the Bedika, and are only doing it in order to exempt the father/homeowner from his search obligation. Since in a case that the father/homeowner himself were to check the areas which the emissaries were appointed to check he would not have to repeat the blessing, being that he had already said the blessing once before, therefore, similarly the emissaries which are doing the mission of their father are not obligated to say the blessing. Nevertheless, Lechatchilah they should not do the Bedika without hearing the father/homeowner say the blessing, as otherwise they are doing a Mitzvah without having a blessing precede their mitzvah. [Admur ibid]

Other opinions: Some Poskim rule that the emissaries have to say the blessing if they made an interval or did not hear it said. [Chok Yaakov, brought in M”B 432:11] Some Poskim thus conclude that if the emissary did not hear the blessing, or made an interval, he should not be sent to search, unless it is a case of need that one cannot do the entire search alone. [M”B ibid]

[5] Admur 213:7 in parentheses; Shulchan Gavoa 289:4; Sova Semachos 4; Rav Poalim Y.D. 2:2; Yechaveh Daas 2:32;  Chayeh Halevi 1:94; Shaareiy Mezuzah p. 377; See Sefer Sechel Tov 289:48; Piskeiy Teshuvos 213:2 footnote 12

[6] Admur 213:7 in parentheses; See however, Admur 457:4; Ohalei Sheim 7:103; Shut Tzemach Tzedek Y.D. 235; Yagdil Torah 15:134

[7] Admur 457:4 that so is the Minhag for each woman to say a blessing; See Ohalei Sheim ibid who answers contradiction that here it refers to women and in 213:7 it refers to men; See Koveitz Hearos Ubiurim 798 p. 89

[8] See Admur 263:15; Kuntrus Achron 263:2; Koveitz Hearos Ubiurim 798 p. 85

[9] 1^st opinion in Admur ibid

[10] 2^nd opinion in Admur ibid; Kuntrus Achron ibid

[11] The reason: As they are all obligated in the Mitzvah due to Din Areivus. [Kuntrus Achron ibid]

[12] Admur ibid

[13] Admur 585:8; See Admur Kuntrus Achron 263:2; Koveitz Hearos Ubiurim 798 p. 85

[14] Admur 213:7 in parentheses; Michaber Y.D. 265:5; Tur 265; Shut Harosh 64 in name of Rabbeinu Simcha