Is the questioner entitled to demand his right from his partner and his brothers, knowing that he lost part of his capital due to the non-payment of one of the checks after the division of payments among them?

If you have agreed to divide the checks, and your right has been delayed due to the crisis, this does not invalidate the division. You are not entitled to revoke it and share what your brothers have taken, except with their consent. Your right remains a debt owed by the man. If he is in hardship, grant him a delay until a time of ease, according to the Almighty's saying: "And if there is one in adversity, then [let there be] a delay until a time of ease. But if you remit [it] as charity, it is better for you, if you only knew." And for the hadith: "There was a merchant who used to lend money to people. If he saw someone in hardship, he would say to his young men: 'Forgive him, perhaps Allah will forgive us.' So Allah forgave him."