Q. Is s’s’ the correct plural possessive form of s? It’d be used to show that a group of s’s owns something/multiple things. If not, could you explain why it wouldn’t work (same with if it does work)?
A. Well, yes, your example is technically correct (we applied italics to three instances of the letter s in your question). The plural of the letter s is formed with an apostrophe for the sake of clarity: s’s. The possessive form of a plural that ends in s takes an apostrophe alone: s’s’.
But for the sake of your readers, not all of whom will enjoy deciphering a four-character term that relies on a mix of italics and regular text plus two different kinds of apostrophes—the first of which, for the plural s’s, can also mark the singular possessive (which is identical: s’s)—consider spelling out the letter s, as in an ess’s curves (singular possessive) or a group of esses’ curves (plural possessive).
See also CMOS 7.15 (on the plurals of letters), 7.16 (on possessives), 7.67 (on letters as letters), 7.70 (on letters as shapes), and 7.71 (on the names of letters); for periods and commas next to apostrophes, see 6.126.