Are the deceased's children entitled to claim half the loan amount that the questioner took from Al-Bara'ah, knowing that the deceased did not want the full amount and the bank waived the debt?

If you authorize your brother to borrow and repay the loan jointly, his children have no right to demand anything from you, because the bank is the lender. You must contact the bank and inform them of this, as they may require you to pay your share. Sheikh Sulaiman Al-Majid has issued a fatwa stating that whoever is the real mutawarriq (one involved in tawarruq) must pay the installments to the bank even if his brother dies, and he must inform the bank of this.