Does one recite Birkat Ha'lebana (the Beracha recited each month over the new moon) during the observance of the seven-day mourning period, Heaven forbid?
The Magen Abraham (work by Rabbi Abraham Gombiner, Poland, 1637-1683) writes (in Orah Haim 426:4) that a mourner should preferably delay the recitation of Birkat Ha'lebana until after the seven-day mourning period. Thus, if the seven-day period concludes only on the tenth day of the month or later, he should recite the Beracha during the mourning period, rather than risk missing the opportunity to recite the Beracha due to cloudiness. (This Beracha may only be recited during the first two weeks of the month, and only when the moon is visible.).
Accordingly, Rav Shemuel Pinhasi (contemporary scholar in Israel) rules that whenever there is concern that one might miss the opportunity to recite Birkat Ha'lebana by waiting until after Abelut (mourning), he should recite the Beracha during the seven-day mourning period. This is particularly relevant during the winter months, when inclement weather is more common.
The Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909), in his work Rav Pe'alim (vol. 3, Yoreh De'a, end of 31), rules that it is proper to study and teach words of Musar (religious teaching) and the like in a house of mourning, in merit of the deceased. Even though the mourner himself may not study Torah during the seven-day mourning period, it is permissible and appropriate for the visitors to learn in the house in order to bring merit to the soul of the deceased. It is also proper to recite Tehillim for this purpose. Hacham Ovadia Yosef follows this opinion in his work Yabia Omer (vol. 4, Yoreh De'a, 23).
If a Minyan prays in a mourner's home on Rosh Hodesh, Hallel is recited. It is customary for the mourner or mourners to step out of the room while the rest of the congregation recites Hallel.
The Kaf Ha'haim (work by Rav Yaakob Haim Sofer, 1870-1939), in Siman 128 (262), cites different views regarding the recitation of the paragraph, "Elokenu V'Elokeh Abotenu Barechenu" in a house of mourning when no Kohanim are present. Rav Pinhasi rules that the accepted practice is to indeed recite this paragraph in a house of mourning if no Kohanim are present, just as in the synagogue. He adds that this would also apply in a case of a congregation that does not have the practice to recite Birkat Kohanim on weekdays.
Summary: A mourner should preferably not recite Birkat Ha'lebana during the seven-day mourning period, unless he is concerned that the delay might cause him to miss Birkat Ha'lebana altogether. It is proper for visitors to study Torah and recite Tehillim in a house of mourning. If a Minyan is held in a mourner's home on Rosh Hodesh, the mourner steps out for the recitation of Hallel, and the others recite it as usual. Birkat Kohanim is conducted in a house of mourning as usual, and if no Kohanim are present the Hazan recites "Elokenu V'Elokeh Abotenu Barechenu."
