A. Possessive nouns usually are formed by adding an apostrophe (') and s. For Example : Ram's book / Grandma's mirror
B. When a noun is plural and ends in s, just add an apostrophe ('). For Example : The kids' toys. / My parents' house
C. If two people own one thing, add the apostrophe and s to the second person only. For Example : Ram and Shyam's new house / Tom and Doug's car
D. If two people own separate things, add the apostrophe and s for each person. For Example : Sita's and Gita's books / Ben's and Jim's offices