Q. Can an onen (one who lost a close relative, before burial) be a sandak at the bris of a grandchild?
A. Chidushim Uviurim (11) maintains that if the body of the deceased has already been transferred to the Chevra Kaddisha, it is permitted. (See also Mourning in Halacha 5: 46).
Horav Shlomo Miller’s Shlit’a opinion is similar. The Rov added that the onen should depart after the bris and not stay to be greeted with mazal tovs and brochos.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a