Why is Josh eating those Candie's when he's introduced as Beta?

He's actually an omega

Ya but they dont know
So him eating those candies its kinda weird lol

No, it would be weird if he didn't. Extreme alphas can turn betas into omegas with their pheromones. There is a reason the guards for extreme alphas are gammas, but even they need a break. And they are using the candies too, to hold out longer. It was explained in the novel.

Then why their team Captain eating those Candie's?

*Not eating

idk why but i think this novels world, beta can smell the alpha and Omega's scent too.

Hmm, you mean "don't eat"? We don't see if he eats them or not. But since even Gammas are eating them, who can't smell the pheromes, the team leader most likely eats them, too.