Nature and Privatization

In the first paragraph of 'Private Property and Communism', Marx and Engels equate Private Property and Division of Labor, and by classifying them as "natural", apparently oppose Rousseau's concept of Nature. On the other hand, in the next paragraph, they posit that a "communal interest" that exists "first of all in reality", undergoes a "cleavage" of individual interest from general interest "as soon as" privatization occurs. Now, "as soon as" implies that what they call "natural" is subsequent to an initial condition that Rousseau calls "natural". So, there is a confusion in these passages that could benefit from a standard methodical treatment that includes a definition of 'nature', and an explanation of how that concept relates to Rousseau's.