The Shulhan Aruch rules that one must drink a "Melo Lugmav" – a cheekful – of the wine in the Kiddush cup. This is equivalent to the majority of a Rebi’it (3.2 ounces), or approximately 1.7 ounces.
According to the Shulhan Aruch, the Mekadesh – the person who recited Kiddush – should be the one to drink the wine. The Geonim were of the opinion that if the Mekadesh does not drink the Kiddush wine, then nobody who heard Kiddush fulfills the obligation. Out of concern for this opinion, the Mekadesh should be the one to drink. Therefore, people who are together for Kiddush should ensure to appoint for Kiddush somebody who is able to drink the wine. Sometimes, people want to give this honor to an elderly man who cannot drink wine. This should not be done, as the Mekadesh should drink the wine.
If, however, for whatever reason, the person who recited Kiddush is unable to drink, then the cup should be given to somebody else to drink. If nobody is able to drink the required amount of wine, then it suffices if everybody drinks a small amount, as long as between everybody the required amount is drunk. This is the ruling of Rabbi Moshe Ha’levi (Israel, 1961-2001), in his Menuhat Ahaba, and of Hacham Bension Abba Shaul (Israel, 1923-1998). They add, however, that if the people know from the outset that nobody can drink the complete amount, they should recite Kiddush over bread rather than recite Kiddush on wine and have everybody take a small sip.
There is a debate among the Halachic authorities as to whether the Misva is fulfilled if the wine is drunk by somebody who was not participating in the Kiddush – such as if he had already recited Kiddush earlier – but happens to be present. The Shulhan Aruch writes that "Ehad Min Ha’mesubin" ("one of the people at the meal") may drink the wine, and the Mishna Berura (Rav Yisrael Meir Kagan of Radin, 1839-1933) understood this to refer only to those who heard Kiddush to fulfill their obligation. If somebody who did not hear Kiddush to fulfill the Misva drinks the wine, the Misva is not fulfilled. Hacham Bension Abba Shaul, however, disagrees, and maintains that it suffices for anybody to drink the wine, even a person who did not hear the Kiddush to fulfill his obligation.
The person who recites Kiddush should hold the cup with his right hand. Hacham Bension Abba Shaul maintained that even a left-handed person should hold the cup with his right hand, if he can without spilling, in accordance with the position of the Arizal (Rav Yishak Luria of Safed, 1534-1572). This is also the view of Hacham Ovadia Yosef, who noted that the Shulhan Aruch’s position on this matter is unclear, and therefore a left-handed person should follow the Arizal’s view and hold the Kiddush cup in his right hand.
Although the Misva is fulfilled even if just one person drinks a "Melo Lugmav" of the Kiddush wine, nevertheless, it is a Misva for everyone to drink some wine from the Kiddush cup.
Summary: Kiddush should be recited by somebody who is able to drink the minimum required amount (1.7 ounces). Nevertheless, if the person who recited Kiddush is unable to drink this amount, somebody else can drink this amount. If nobody present is able to drink this amount, Kiddush should be recited over bread. If, however, Kiddush was recited over wine and nobody can drink the required amount, it suffices if they all drink a small amount such that between all of them they drink the required amount. The one who recites Kiddush should hold the cup in his right hand during the recitation, even if he is left-handed. It is a Misva for everyone to drink some wine from the Kiddush cup.
