Just wondering how much the game companies get from each game bought. Since my family shares some computers, we usually just buy one copy of a game to save money I really liked some of the games though (a LOT) and i'm wondering if buying another copy of the game really helps them out that much.

If not then maybe i'll donate money to them or something, much more direct.

Not a whole lot. It entirely depends on the company. I think it is common practice to give a bonus based on performance of the product, but other than that, they usually have a fixed salary. Coupled with a bonus, the company usually thinks devs can be encouraged to overwork to meet deadlines in order to get said bonus. Your purchase does help them keep their jobs though. The biggest your purchase really does is just that; enhance their job security.

However, I am not an expert so take that with a grain of salt.

It'd depend. If it's an independent developer who doesn't have to pay publisher fees and so on, then I'd imagine they make more than a company who develops a game but has to go to a publisher to back the price of selling it.