The possessive form of the plural noun children is children's.
Example: The children's lunches are ready.
Years'
Uncles'
The word its is a posessive pronoun.
Painters'
The possessive form of "their" is "theirs."
singular
The knife's edge had been dulled when it hit the rock. Knife's is singular posessive. The knives' edges had been dulled when they hit the rock. Knives' is plural posessive.
The possessive form would be "agency's."
The plural possessive of region is regions'.
The singular possessive form of "faculty" is "faculty's."
The singular form of the noun is stapler. The singular posessive form of the noun would be stapler's. The plural form of the noun would be staplers. The plural posessive form of the noun would be staplers'
"To have" as a posessive is the verb "tener". As an auxillary verb, it is "haber", as in "I have gone to the store".