apostrophes
are used to indicate the omission of letters or numbers in words.
For example,
can’t for cannot
he's for he is
class of '99 for class of 1999
it's for it is
(note: never 'it's' to denote possession - the possession is implied by definition. Placing an apostrophe in 'its' when denoting possession is incorrect)
Apostrophes are also used to indicate possession. In this case, the apostrophe takes the place of the word 'of'. That is, if you reword the phrase in question to include 'of' to denote possession, the correct placing of the apostrophe becomes obvious, even in those so-called tricky cases of placing apostrophes to words ending with s.
For example,
Harry’s book - the book of Harry
fws's values - the values of
fws
the boys’s coats - the coats of the boys
Where there are two people sharing possession of one thing, the two people are treated as a single unit, so only one apostrophe s is used.
For example,
Hannah and Ben's dog, not Hannah's and Ben's dog - the dog of Hannah and Ben
or
Gilbert and Sullivan's operettas - the operattas of Gilbert and Sullivan
Where there are two people possessing separate things, individually, each person receives their own apostrophe s.
For example,
If you are talking about books that two people have written (separately, not as co-authors), each person would need an apostrophe:
John Updike's and Anita Desai's novels are widely read - the novels of John Updike and the novels of Anita Desai are widely read.
or
Rudd's and Howard's beliefs
Possessives, such as its, theirs, and ours never carry apostrophes. Why would they? Only to denote possession, but the possession is implied by definition.
For example,
fws is happy with its progress.
The Kesho Krew feel, that as far as development projects go, theirs is the best.
Ours will always be a well-supported organisation.