First of all Poland has bilateral agreement with Brazil, so you can come here as a tourist without any visa. Moreover when the allowed time in Poland finishes you can leave the country for example by crossing Ukrainian border and come back again. It's the same agreement as mentioned here in the topic about USA: https://polishforums.com/usa-canada/poland-bilateral-visa-waiver-agreement-69842/
If you want to come here with business visa, then requirements are following:
You must open 1 of the following types of the company in Poland:
- limited partnership
- limited joint stock partnership
- limited liability
- joint stock company - limited liability company
Only problem (except of the bureaucracy) is that those forms of business are relatively expensive.
You have to pay 50 000 pln or 100 000 pln for establishing company. And later pay for accountant to do bookkeeping.
There are other forms of companies in Poland, but not available for foreigners. Advantage of those is limited liability - up to the amount payed for establishing the company.
Another idea is for your brother to open cheaper form of the company and employ you.