Tosafot (Pesachim 99b, s.v. lo [#2]) discuss the possibility of fulfilling the four cups of wine by having one set for the head of the household, and having all the family members discharge their obligations through him, as is generally done for Kiddush. By contrast the implication of the Rambam (Hil. Chametz U’Matzah 7:7) is that every family member requires their own set of four cups.

As the Brisker Rav (Chiddushim to the Rambam) and others explain, the issue appears to be the question of what exactly is mandated by the obligation of the four cups. On the one hand, it may be that the Rabbis mandated that wine be consumed at the seder, as a symbol of freedom. Four would thus parallel of the “leshonot shel geulah” (expressions of redemption found in the Torah). Alternatively, the obligation may be to recite the four speech-related commandments of the seder – Kiddush, Haggadah, Birkat Hamazon, and Hallel – in the presence of wine.

Thus, the Rambam would accord with the view that the obligation is to drink wine. Consequently, there is no role for “shomea k’oneh” (listening is as speaking), as the mitzvah is a physical mitzvah that by its nature must be done by the individual himself. Tosafot, however, see the obligation as requiring recitations over wine, and thus the model of Kiddush is appropriately relevant.

It should be noted that even Tosafot, in their conclusion, recommend a separate set for each member of the family. Further, as indicated by the Resp. Hitor’rut Teshuvah (I, 246:1), it might be suggested that Tosafot’s suggestion was particular to the context in which the comment was made. The Mishnah had stated that even one who is supported by public funds must ask for charity to purchase the four cups. This stringent approach is reflective of the need for “pirsumei nisa” (publicizing the miracle). It may be that Tosafot’s point was that pirsumei nisa can be accomplished with one set per household. The full obligation, however, would require one set for every family member; nonetheless, once pirsumei nisa is satisfied, the obligation of the four cups does not mandate taking for charity for its fulfillment.