Grammar: Demonstratives

"yo" is an indicator of the plural form.

bear with me please :)

examples:

liv la → the book (singular)

liv yo → the books (plural)

ti gason an → the little boy (singular)

ti gason yo → the little boys (plural)

kay sa → this house (singular)

kay sa yo → these houses (plural)

moun sa → this person (singular)

moun sa yo → these people (plural)

So...

Sa se kreyon mwen. → This is my pencil.

Sa yo se kreyon mwen → these are my pencils.

Sa se yon radyo. → This is a radio.

Sa yo se radyo. → These are radios.

Liv sa se pa m. → This book is mine.

Liv sa yo se pa m. → Those books are mine.

Mesye sa se frè m, → That guy is my brother.

Mesye sa yo se frè m. → Those guys are my brother.

Mwen renmen foto sa. → I like this picture.

Mwen renmen foto sa yo. → I like these pictures.

Mwen pa konprann mo sa. → I don't understand this word.

Mwen pa konprann mo sa yo. → I don't understand these words.

FYI:  The word "yo" just like the other Haitian Creole pronouns can be confusing. 
"Yo"  is the plural definite article → as in:  liv yo - the books
"yo" is the subject pronoun → as in:  Yo pale - they talk
"yo" is the object pronoun → as in:  Mwen renmen yo - I love them
"yo" is the possessive adjective → as in:  Sa se kay yo. - This is their house.