My understanding is that even though someone may normally have their entire extended family each year for Purim Seuda (eg their sisters who are also Aveylot) and their children, it is better to have the Purim Seuda only with one’s immediate family during Aveylus. That is, wife and children. Is this correct? If so, what does this mean in regards to Pesach Seder where a similar situation has always been in practice. Should one break up into private home Sedarim (in Chul) and not get together with sisters or brothers and their families as per the past? If so, what does it mean for a Shabbos meal. Should one not ever invite one’s sisters and their children (the sisters are Aveylot and I am an Avel all after Shloshim) for a Shabbos meal? Perhaps if we do so because it’s a birthday, that’s not a good practice, but doing so Stam, as a family unit is okay, but perhaps it’s not preferred?

Shalom, Thank you for your question - may you be blessed with only good news, and long life for you and the whole family. The laws of those in the year of mourning partaking in celebratory meals have many different opinions about them. I will try to outline here some of the major rulings on these issues. With regards to the Purim meal, in the work Mikray Kodesh of Rav Harari, he quotes the rulings of Rav Moshe Feinstein zt"l as follows "The mourners are allowed to invite family to their Purim meal, even those who are not in mourning. And if they want to invite the spouses of those in mourning, and the spouses are not themselves in mourning, then only if there will be altogether 3 or 4 guests at the meal, because then it is not considered as a "meal of friendship" (se'udat mera'ut), but rather only as guests, and is thus permitted. There is permission to be more lenient and rely on the opinion of the Shach, but it is better not to do so." In the work Piskay Tshuvot (696,7) "... In the year of mourning for one's parents, and within 30 days for other relatives, if one is accustomed every year to have the Purim meal and be happy on Purim with one's friends, one is allowed to attend such a meal on condition that there are no musical instruments played there and one does not join in the dancing." As we will see below, when the meal is in the mourners house, the halacha is even more lenient. From these two sources we see that there no clear agreement on the exact level of meal that is allowed. If you have a custom to hold the Purim meal in your house each year with the extended family you may continue the practice even in the year of mourning, but there is room to be strict and have a smaller gathering this year with the immediate family and relatives who are themselves in mourning (and their spouses). There are no restrictions on attending the Passover Seder, or inviting to your home guests. The mourner is permitted to eat regular Shabbat meals at a friend's house, or to eat with a group of friends at the Third Meal. Even if this meal continues into the night following the Shabbat, this is permitted. (Mourning in Halacha - R. Goldberg, 25:15). All the more so may the mourner invite guests to a regular Shabbat meal in their home. (ibid 25:13). Blessings.