Longman & Broderip began as just Longman & Co, founded by James Longman in 1767. The firm began selling music and instruments made by other piano makers, Longman never made pianos himself. The firm did not sell pianos alone, they also sold other stringed instruments such as violins, violas, and cellos. One such piano maker who constructed pianos for Longman was Christopher Ganer, a well known square piano maker. In 1769 Longman & Co partnered with Charles Lukey and the firm was known as Longman, Lukey & Co until 1775. In this year the duo was joined by Francis Fane Broderip and for only a year the firm was called Longman, Lukey & Broderip. The next year Lukey left the firm and Longman & Broderip persisted until 1798, when the business suffered and underwent bankruptcy. Fortunately, the firm survived as Longman, Clementi & Co when Muzio Clementi invested in the business, however this only last for two years as Longman left the firm in 1800.
Literature References:
Clinkscale, M., 2006. Makers of the piano, 1700-1820. 1st ed. Oxford: Oxford University Press, p.182.
Palmieri, R. and Palmieri, M., 2003. Encyclopedia of Keyboard Instruments. 2nd ed. New York: Routledge, p.224.