Let's explain each statement in detail:

1. "They build nests by making burrows in the ground."- This statement is incorrect. Indian squirrels are actually arboreal, this means they live in trees. They are known for building their nests, called dreys, in trees using twigs, leaves and other materials. They do not make burrows in the ground.

2. "They store their food materials like nuts and seeds in the ground."- This statement is correct. Similar to many other squirrel species, Indian squirrels do practice food hoarding. They store their food (like nuts and seeds) in various places, which can often include burying them in the ground, especially when preparing for periods when food will be less available.

3. "They are omnivorous." - This statement is correct. Indian squirrels are mostly herbivorous, eating primarily a diet of nuts, seeds, fruits, and buds. However, they have been known to eat insects, small birds, and bird eggs when the opportunity arises, which technically makes them omnivores.

Therefore, based on the above explanations, out of the three statements provided, two are correct (the second and third statements).