Q. If a couple are married on the Sunday before Pesach and there are no further Shevah Brochos on the following weekdays, can one say Shevah Brochos on the two Seder nights (Friday and Shabbos) of that week?
A. Poskim agree that there is no obligation to perform all sheva brochos (Yam Shel Shlomo, Kesuvos 1,12, Maharil, Rav P’olim E.H. 4,6, Aruch Hashulchan O.C. 640,14 -et al.), and they mention different traditions in that respect, doing all sheva brochos is the most widespread.
When sheva brochos are recited during the Pesach Seder, in order to avoid adding more cups to the mitzvah of drinking only four cups and at the same time circumventing the predicament of bundling many mitzvos together (which belittles them), a number of practices have been suggested.
Darkei Moishe (473,4) suggests that the mezamen should use his cup when leading bentching, while the sheva brochos should be recited on the groom’s cup, (for that matter any other cup). Igrois Moishe (E.H. 95) recommends following this opinion.
Mishne Halocho's (11, 382) counsel is that the chosson himself should not recite any of the sheva brochos, even if his cup is being used.
Chida (Chaim Shoal 74,13) advices to do bentching and sheva brochos on the same cup.
Kaf Hachaim (479, 3 quoting Birchos Maim) opines that one of the attendants should lead bentching, while another recites sheva brochos on his own cup, then the one who leads says, "bore pri hagofen" on his cup.
Yavet'z (Hagadah on his Sidur) maintains that two cups should be used, and the one of sheva brochos should be kept for use as the fourth cup.
Horav Shlomo Miller's Shlit"a opinion is to follow Igrois Moishe's decision quoted above.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit"a
It seems to me that the questioner should be informed, as part of the answer, that if the wedding takes place on Sunday April 1 before sunset (9 Nisan) then they can say Sheva Brachos during the first Seder on Friday night and at any meals during Shabbos day, but they cannot say Sheva Brachos at the second Seder on Saturday evening, as that will be after the end of the seventh Jewish-calendar day from the wedding, counting the wedding day as the first day.