For non-count things separately possessed - use apostrophes for each possessor: Mary's and Bill's money (Mary's money and Bill's money). For non-countables shared or held in common, use an apostrophe for the last possessor only: Mary and Bill's money (the money which Mary and Bill own jointly). The investors and businessmen's trust.
Sometimes possession is shared by several nouns. In these cases, just
make the last word in the series possessive.
America and Canada's timber resources are dwindling
Thomas and French's discovery shocked the world.
Leslie and Eric's lasagna is to die for.
These sentences all contain nouns that show joint ownership. In the
first sentence, the resources belong to America and Canada. In the
second sentence, the discovery belongs to both Thomas and French. In
the third sentence, the lasagna belongs to both Eric and Leslie.
To show individual ownership, apply the possessive sign to each item
in the series.
America's and Canada's timber resources are dwindling
Thomas's and French's discoveries shocked the world. [Note: I
personally would have used Thomas' instead of Thomas's.]
Leslie's and Eric's lasagnas are to die for.
In these examples, each noun has individual ownership of resources, of
a discovery, or of a lasagna. These things are not shared.
"Possessive Case" in The Grammar Bible, Michael Strumpf, Macmillan (1999) page 29