Q. Can someone observing Avelus during Shloshim (the first Thirty Days) attend during Shabbos a Sheva Brochos meal of a family member in a shul, to which he also contributed?
A. See Shulchan Aruch (Y.D. 391: 2) that one should not attend a festive meal outside of his home even for a close relatives, while he is still during the first thirty days of mourning.
Horav Shlomo Miller’s Shlit’a opinion is that it is advisable not to attend.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller and Horav Aharon Miller Shlit’a