1. When two or more singular nouns are joined by ‘AND’ the Pronoun for them always in the plural number.
Ex.- Mohan and Sohan have lost their books. (Correct)

2. When two or more singular nouns joined by ‘AND’ are preceded by ‘EACH’ and ‘EVERY’ the
pronoun must be singular.
Ex.- Every student and every teacher took his or her seat.
Each of Ram and Shyam has done his work.