I think Engels best works were the little Essay On Revolution (it's 'not a tea party' but the violent repression of one class by another), Utopian and Scientific Socialism (Socialism is not a pious wish, but presaged in the material development of society), Ludwig Feuerbach and the End of Classical Philosophy (clear account of the origins of Marxism) and The Force Theory of History (a good anticipation of a critique of Michel Foucault ). He read English political economy before Marx did (Outlines of a Critique of Political Economy), and Condition of the Working Classes in England was a big influence.
David Macgregor says that his family firm was prosecuted more than once under the factory acts, perhaps adding to Marx's knowledge of them (Macgregor, David, Hegel, Marx and the English State, Toronto University Press, 1996)
I can remember reading about the final insolvency of the Engels family firm, probably in the Yorkshire Evening Post, in the late 70s or early 80s.