Questions & Answers about Mój brat ma własną firmę i pracuje sam.
Why do we use sam here instead of another form?
Sam means "alone" or "by himself". It behaves like an adjective, which means it has to agree with the subject of the sentence. Since the subject is Mój brat (a masculine noun), we use the masculine singular form sam. If the sentence was about your sister, it would be Moja siostra ... pracuje sama.
Why does firma change to firmę and własna to własną?
This is the Accusative case, which we use for the direct object of an action. The verb ma (has) requires this case for the thing being owned. For feminine nouns ending in -a, the ending changes to -ę (firmę), and the adjective describing it changes its -a to -ą (własną).
Could I use swoją instead of własną in this sentence?
Yes! Swoją (one's own) is completely correct here because the brother is the subject who owns the company. However, własną is a bit stronger—it specifically emphasizes that it is his very own business, which pairs perfectly with the fact that he works alone.
Does sam just mean "alone" here, or "by himself"?