Speaking as a guy whose last name is Jones, I can tell you with some authority that the correct way to make a singular noun possessive is to add 's, EVEN IF THE NOUN ENDS WITH AN S. Please, please, please spell my name correctly in the possessive.
The possessive of “Mr. Jones” is “Mr. Jones’s.” It is pronounced the sames as “Joneses.”
The possessive of “The homeless” is “The homeless’s.”
The possessive of “Beatles” is “Beatles’” because that’s not a singular.
However - sigh -
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Most authorities agree that making a singular noun that ends with an S possessive can be done with just an apostrophe if for no other reason than it’s common right now,
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As has been pointed out, some authorities (inexplicably and illogically, to me) make it conditional on whether the word is followed by a word that starts with S, and
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“Homeless’s” sounds really funny to me. I can’t imagine any place you’d have to write that that you couldn’t come up with a better construction. At least to me, “homeless” is better used as an adjective, not a noun.