(This should not be relied upon for practical halacha. When a question arises a Rabbi should be consulted.)
1. The poskim tell us that the souls of the departed come to the wedding of their children and grandchildren (see Zohar Pinchas, Shu”t Maharash Engel vol. 7 page 119, Yesod Veshoresh Haovodah Shaar Hakolel 15, and Sefer Minhagim Chabad 75).
2. Many have the custom that if the chosson or kallah have lost one of their parents, the engaged child goes to the cemetery before the wedding to extend an invitation to the parent who is deceased (see Shulchan Haezer vol. 2 page 137 and Shu”t Mishnah Halachos 5:247). Some write that the source for this custom is the Zohar (Minhag Yisroel Torah on Nisuin page 137).
3. It is unclear whether this custom extends to grandparents or other relatives (see Sefer Derech Sicha page 152, Yismach Lev page 55, and Sefer Shaarei Nisuin Miluim 2). The Shulchan Haezer writes that the custom is to invite “the parents and the relatives.” It would seem that he feels that this custom does extend to the grandparents. However, Harav Yosef Shalom Elyashiv zt”l is of the opinion that one need not invite the grandparents who are not alive (Sefer Yivakshu Mipihu page 478).
4. The concept of inviting the departed may be used to explain a very interesting custom amongst Chabad Chassidim. The custom among Chabad Chassidim is that during the kabbalas panim the chosson recites the chassidic sermon called maamer lecha dodi 5689 (Sefer Minhagim Chabad page 75).
The Lubavitcher Rebbe zt”l explains why this maamer is recited. He writes (Toras Menachem vol. 8 page 218), “At my wedding, before the previous Rebbe started saying the Maamer Lecha Dodi, he said, ‘It is well known that at a wedding souls of the fathers come from the World of Truth, going back three generations – and this applies to all Jews – however, there are occasions (by the weddings of Rabbeim) when even more than three generations of souls are present. The recitation of this maamer actually serves as an invitation for these great souls to come to the wedding. A portion of this maamer is from the Alter Rebbe, a portion from the Mittler Rebbe, a portion from the Tzemach Tzedek, and a part from the son of the Tzemach Tzedek (the Rebbe Maharash) the great grandfather of the kallah. A part from the son of the Tzemach Tzedek (Reb Baruch Sholom) the great grandfather of the chosson, and a part from the Rebbe Rashash, the grandfather of the kallah.’ Certainly in the maamer there was something from the Previous Rebbe himself, although he did not state this explicitly. Since we walk in the ways of the previous Rebbe, it is correct that at every wedding (of those who are connected to the Rebbe) that before the chuppah the chosson or another person should say the maamer lecha dodi. Which as aforementioned has a part from all the Rabbeim, and this will serve as an invitation to the souls of all the Rabbeim to participate in the wedding.”
[Following this reasoning, some wish to say the maamer lecha dodi 5714 which is a maamer of the Lubavitcher Rebbe zt”l (and also mentions all the other Rabbeim). This way all the Rabbeim, including the most recent Lubavitcher Rebbe zt”l, will be invited to the wedding.]
Please email any questions or comments to firstname.lastname@example.org