Siman 644
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א שַׁחֲרִית, אַחַר חֲזָרַת תְּפִלָּה, נוֹטְלִין הַלּוּלָב וּמְבָרְכִין: עַל נְטִילַת לוּלָב, וְשֶׁהֶחֱיָנוּ; וְגוֹמְרִים הַהַלֵּל; וְכֵן כָּל שְׁמוֹנַת יְמֵי הֶחָג. וּמְבָרְכִים: לִגְמֹר אֶת הַהַלֵּל, בֵּין צִבּוּר בֵּין יָחִיד, וְאֵין מַפְסִיקִין בּוֹ אֶלָּא כְּדֶרֶךְ שֶׁאָמְרוּ בִּקְרִיאַת שְׁמַע: בָּאֶמְצַע, שׁוֹאֵל מִפְּנֵי הַיִּרְאָה וּמֵשִׁיב מִפְּנֵי הַכָּבוֹד; בֵּין הַפְּרָקִים, שׁוֹאֵל מִפְּנֵי הַכָּבוֹד וּמֵשִׁיב שָׁלוֹם לְכָל אָדָם; וְאִם פָּסַק בָּאֶמְצַע, וְשָׁהָה אֲפִלּוּ כְּדֵי לִגְמֹר אֶת כֻּלּוֹ, אֵינוֹ צָרִיךְ לַחֲזֹר אֶלָּא לַמָּקוֹם שֶׁפָּסַק.
1 The Order of Hallel during the Festival, 2 Seifim: During Shacharit after the repetition of the Amidah, we take the lulav and bless "on the taking of the lulav" and Shehecheyanu and say full Hallel. The same is done on all eight days. We bless "to finish the Hallel," whether with the community or alone. We do not interrupt during it except for the ways that are done during the reading of the Shema: in the middle [of a section] we greet somebody who we fear and respond to somebody who we respect, and between the sections we greet somebody who we respect and respond to anybody. If one interrupted in the middle with enough time to say it all, they do only need to return to the place that they stopped.
ב בְּהַלֵּל אֲפִלּוּ עֲשָׂרָה קוֹרִין כָּאֶחָד.
2 During Hallel, even ten people can sing at the same time.