1,357. When a Mourner May Participate
212:3 If the mourner is the sandek (the one who holds the baby) or the mohel at a bris and it is after shloshim, even for a parent, he may wear Shabbos clothes until after the bris and he may eat at the festive meal.
212:4 A mourner may not enter a wedding hall during shloshim for most relatives, nor during the twelve months of mourning for a parent, not even to hear the brachos. However, if a wedding is being held in the courtyard of a shul and they recite the brachos there, then the mourner is permitted to stand and listen to the brachos after thirty days even for a parent. The mourner may recite the wedding brachos, serve as attendant to escort the groom to the chuppah, and wear Shabbos clothes after shloshim, though he may not enter a wedding hall in order to eat at the meal. Some authorities are lenient even when it comes to the wedding meal.