I'm going to assume by being "the company manager" you hold the highest managerial position of the company, and the "manager" you refer to is the owner of the company.
If by "tell the company owner what's really happening" you mean that you'll explain to the owner that credit for your work is being stolen, you can expect to get called childish and ignored. You shouldn't assume for one second that the owner is not aware about what is going on.
You need to frame your concerns in terms of negative impact to the business. How does the behaviour of your owner and their friend cause risk to the operations? The owner is, of course, allowed to run their business however they see fit, so you need to make sure the owner knows they are making a decision between success of the business and nepotism.
EDIT: I've just taken a look at some of your other questions. I'm assuming this is the same company. I don't say this often, but you have to really assess if you wish to continue working here.