Plural, as far as I know, uses 's (5) for possession, unless the plural ends with s (6), then it uses just the apostrophe?
If a plural ends in
s, then the apostrophe follows it with no additional
s.
Singulars ending in
s or an
s sound are more tricky.
When forming the genitive of a singular word ending in
s, there is (and I quote
The Oxford Guide to Style, formerly known as
Hart's Rules) "no single rule", and "Euphony is the overriding concern", e.g.:
the hiss's sibilance;
the miss's hat;
The scissors' point;
the scabies' transmission. In UK English (as opposed to US) there is a tendency to transpose these phrases to use
of rather than an apostrophe.
Names ending in
s have rather complex rules (in the same book) depending on whether they are classical (no added
s, e.g.
Heroditus') or not. My name and my son's are not classical, and so the genitive has another
s:
Hodges's,
James's; but for longer non-classical names, the
s may be considered optional, so my other son can have
Nicolas' or
Nicolas's to taste. In the specific case of
Jesus, either form is equally acceptable.
There is more, but I'll stop there.