Whether it be two or seven blessings, do both the bride and groom need be present for sheva brachos?
The Yam Shel Shelomo (Kesuvos 1:20) writes that the brachos are primarily directed towards the chosson, and so if the bride is not present then they may still make all seven brachos, as long as the groom is there. The China v'Chisda on Kesubos (vol. 1, p. 113b) agrees, though he quotes the Ritva as holding that both the bride and groom must be present. He also quotes (later, vol. 3 p. 272b) from others that even if the groom was not present for some reason, but the meal was still prepared in honor of the couple, some say that Sheva Brachos can be made, and apparently that was the custom in Salonica.
Rav Ovadia Yosef in Yabia Omer 6:9:1-2 brings many sources (כדרכו) as to what to do in such a case, and concludes that the Shulchan Aruch appears to hold like the aforementioned Ritva. Therefore, both the bride and groom must at least participate in the meal, and although strictly speaking the bride can be in a different room, it is best for her to be brought in for the brachos (see also Yalkut Yosef Sova Semachos 1, 16:3, 16:8)
Apparently such a case occurred in 19th Century Nikolsburg, where the groom left for a business trip into his Sheva Brachos week. This case is discussed in both Teshuvas Mahari Asad (no. 12) and Maharam Shik (no. 90), who both believe that Sheva Brachos should not be made in such a case.
According to many contemporary Poskim - Rav Ovadia (Yabia Omer vol. 6 Even HaEzer 9), Rav Mordechai Eliyahu (“Hilchot Shidduchim and Chatunah” by R’ Shmuel Eliyahu), Rav Moshe HaLevi (Birkat Hashem (vol. 4 page 246)), and the Tzitz Eliezer (vol. 13 Siman 99) - if the Chattan and Kallah were both present and ate bread at the beginning of the meal, the guests may recite Sheva Berachot, even if one or the other left in the middle. If, however, one of them was not present at the beginning or didn’t eat, Sheva Berachot may not be recited. See also Shalmei Simcha page 323, 355.
Rav Vozner holds that although it’s ideal for the Kallah to hear the Berachot, if she is not present during the Seudah, Sheva Berachot may still be recited if she feasts with her entourage separately and then comes with them to Birkat HaMazon. It’s questionable if they may do so if she doesn’t enter the room, even if hears the singing from outside. (Shevet HaLevi vol. 8 Siman 281)