Do we have to bring in Shabbat early if everyone else is?

A few months ago I wrote a post about Early Shabbat. One of the important outcomes of that blog post was to note that one cannot bring in Shabbat earlier than the time listed. For example if candle times are listed as 7:28-8:49pm, if one lit Shabbat candles at 7:15pm and made a beracha on them not only would one not be taking on Shabbat it would also be a beracha levatala - Taking Hashem's name in vain since it is too early to bring in Shabbat the blessing cannot be said at that time. 

(There are a few poskim that allow candle lighting before Pelag under certain conditions but they are not mainstream positions and are only relied upon in extremely northern latitudes.)

One area we didn't touch upon was, can individuals, families, or groups bring in Shabbat later/on time if the majority of the community is bringing in Shabbat late? What happens if there is no minyan in the community praying at the normal time (18 minutes before sunset) does that mean a person has to taken in Shabbat early? Are they forced to comply with the rest of the community?

The Mordechai is the first person to address this question. Hew writes that if the majority of the community has accepted Shabbat (early) the minority must follow them regardless." This position is brought by Rav Yosef Caro in his commentary Bet Yosef (O.H. 263.12) to the Tur and He codifies it in the Shulkhan Arukh in paragraph 12 of that same Chapter.

The Kaf HaChaim (O.H. 263:76) and Mishna Berura (O.H. 263:51) quote the Magen Avraham who limits the scope of Rav Caro's ruling writing "Where there are many synagogues in a city, one synagogue need not follow the practice of any other, even if one of them consists of the majority of the community." 

This implies as long as there is a synagogue minyan praying at the regular/late time individuals can bring in Shabbat at that time even if the majority of the community decides to bring Shabbat in early. However, the Mishna Berura and Kaf HaChaim quote the Hayei Adam that "If one gathers a minyan and holds services in his home, even if it is a regular minyan, they are subordinate to the majority and must follow their practice." 

Rav Moshe Feinstein writes (Igrot Moshe O.H. 5:15) that a congregation with two minyanim can have a later minyan in the Summer time even when the majority is praying at the earlier time. The question was asked about Bridge Lane Beth HaMedrash in London.

The bottom line is that there needs to be at least one synagogue minyan that prays late/regular time in the Summer in a community. In Seward Park we find the situation where there is only one late minyan at BCMH and the numbers are tight. We should make every effort to support it especially if you are a person who likes to bring in Shabbat at a later time in the Summer.