Yosef Karo

“ There are those who permit the mourner to eat at a wedding meal or at a Bris with the servants, but only if it is not at the place of joy, for example, at another house. And there are those who forbid this, and such is the custom. Rather, the mourner should do some service there, if he wants, and eat in his house from what was sent from the meal. ”

“ A mourner is prohibited in joy; therefore he should not take a baby in his bosom all of Shiva, because perhaps he will come to levity.
Seif 2: For all dead one enters the drinking house after 30 days ”