If a Chosson & Kallah during the first week they got married attended a Bris, should the assembled recite Sheva Brachos after Bentching?
This case comes up in the Rishonim, and the answer is simply no, the Seudah must be made Lichvod Chattan veKallah to be considered Simchat and Beit Chattanim. Birkat Hashem (vol. 4 page 345), Shalmei Simcha page 347, Shevet HaLevi (vol. 10 Siman 247:3)
Young Israel of North Belmore's Practices and Procedures for Sheva Bruchos says the meal should be prepared specifically for the bride-groom, and as such would not be recited at a Brit.
no sources in the doc though.
EretzChemda.Org quoting B'mareh Habezek 7 says a Sheva Brachos and Bris may be combined. In the notes he mentions Yechave Da'as 1:90 and B'Tzeil Hachochmo 1:68.
I'm not a rabbi...
My assumption is that the sheva brachot (well, six) should not be recited, because the s'udat mitzvah is not in honor of the chatan and kallah; rather, it is for the mitzvah of milah.
A more interesting question, IMHO, would be, if the parents of the baby boy finally got married after he was born, should they say sheva brachot at the brit. Not a very common occurrence.