How would you show possession for it? IE,

The company's owners, IT'S supervisors...........

Is this correct?

That is unfortunately incorrect. This is an often confused part of grammar.

It's = It is or It has
Its = A possession of it

So saying It's supervisors is saying It is supervisors.

The company's owners, its supervisors...

That is the correct form of what you're trying to say.

For more information check out: its and it's - the difference