The Coca-Cola Company and PepsiCo are completely separate companies. Their lead products are similar, but they have been direct competitors since the early 20th century.
Given the size of both companies and their majority shares of the soda and snack food market, it is unlikely that they could be parts of the same company. Anti-trust and anti-collusion laws exist across the world and prevent corporate entities from manipulating the market to their benefit by holding majority control or sharing information to that effect. Other beverage groups, such as Dr. Pepper Snapple, control enough of the market to prevent stagnation between the two larger competitors.