Doubt

user's - one user; e.g. The user's account is closed.
users' - many users; e.g. All users' accounts are now closed.
student's - one student; e.g. The student's grades were very good.
students' - many students; e.g. The third grade students' teacher is kind.
father's - one father; e.g. My father's car is green.
fathers' - many fathers; e.g. The fathers' responsibilities are gr

we usually say that

my fathers' name is john....

does it mean many fathers?

Pronunciation-wise, there is no difference between father's and fathers', and so even when you think you have said fathers', people will usually interpret that to mean father's, as it is the norm for people to have just one father.

If you did that by writing, it would have been a mistake.

Correct:

My father's name is John.

for example

1.this is smith's property.

2.this is smiths' property.

which one is correct?

I am not sure which is the scenario

1) There is someone named Smith, in which case you should capitalize the S in smith.

This is Smith's property. (there is someone named Smith, and this belongs to him/her)

2) There are many smiths (people who work with metals), and this is their jointly owned property.

This is the smiths' property, and it is next to the rach

ooh, I missed scenario #3: there is a family of Smiths.

3) This is Smiths' property. (This property belong to a group of people sharing the name Smith)