Q. If on Erev Shabbos Chanuka it is already close to the shkiah, how many people is the minimum needed to light the shul menora with a brocho?

A. Mishna Berura (671: 47) quotes Darkei Moishe that the hadlaka should be at the time that people begin to assemble in shul. However. if it is late, one should not wait any longer, and perform the hadlaka immediately, since a minyan will eventually assemble and there will be pirsumei nissa (publicizing of the miracle) later on. (Magen Avrohom ibid. 12)
Sha’arei Teshuva (ibid, 12), Mor Uketzia (ibid,) Machazik Brocho (ibid. 7) and others rule that on a regular day one should not light in shul without a minyan. However, on Erev Shabbos, when close to the shkiah one should not wait. Nitei Gavriel (41: 9 n. 15) maintains that it is better not to recite a brocho if there is no minyan in shul yet, since as it is, some Poskim assert that no brocho is said in shul at all. (Shibulei Haleket 185, Maharam Shik Y.D. 10 quoting Chasam Sofer)
Horav Shlomo Miller’s Shlit’a opinion is that even a single individual can do the hadlaka in shul when late with a brocho, when a minyan will assemble there later.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a