The Gemara in Masechet Eruvin, Daf 79 establishes that when one recites Kiddush on Shabbat, he must drink at least the amount of "Rov Revi'it" (the majority of a Revi'it), which in contemporary terms is 45 grams, or a bit more than 1.5 oz. Although ideally one should drink a full Revi'it, he nevertheless fulfills his obligation if drinks at least the amount of "Rov Revi'it."
If the person who recited Kiddush cannot drink this amount of wine, then, according to Maran (author of the Shulchan Aruch), he may give the cup to somebody else immediately after Kiddush, and have that person drink the required amount in his stead. Maran writes that if each person at the table sips a small amount such that in all a "Rov Revi'it" was drunk, this suffices, Bediavad (after the fact), for the fulfillment of the obligation of Kiddush.
However, Rabbi Moshe Halevi, in his work "Menuchat Ahava," rules that there is a more preferable option, without having to resort to reaching the amount of "Rov Revi'it" through the collective drinking of the entire group. In his view, if a group knows ahead of time that no one person in the group is capable of independently drinking the minimum required amount of wine, then they should recite Kiddush over bread. Reciting Kiddush over bread is a more preferable option than having everyone drink a sip of wine so that a "Rov Revi'it" is drunk.
The following, then, are the options for drinking the wine of Kiddush, from the ideal practice to the least preferable practice:
1) The one who recites Kiddush drinks a complete Revi'it of wine;
2) The one who recites Kiddush drinks a "Rov Revi'it" (just over 1.5 oz) of wine;
3) Somebody other than the one who recited Kiddush drinks the minimum required amount;
4) Kiddush is recited over bread;
5) Everyone sips a small amount of wine so that collectively the minimum required amount is drunk.
