As the saying goes, brothers are even, because there are many cases where brothers turn against each other when doing business together, so it is best to separate.

But as your girlfriend, you'd better stay out of it. Try to let them solve it themselves. People are flesh and blood, brothers and sisters, you are an outsider, clothes. Talking too much will arouse suspicion. My brother's girlfriend should fulfill the obligation of reminding him, and must not tell him in front of his brother, but in private without his knowledge. After expressing your opinion, emphasize that this is your own opinion, and let your brother take the big idea himself. In short, be careful not to let outsiders and his family think that you are breaking up and ruining the feelings between the two brothers.