Does the new shop, bought through a usurious loan taken out by my brother, become forbidden for me, knowing that my father willed for the shop to be divided between us?

If your brother's borrowing with usury is contingent upon your approval, then it is not permissible for you to agree, as it involves causing and assisting in sin. However, if he will borrow in any case, then there is no harm for you in benefiting from the borrowed money or from the shop purchased with it, because the sin of usury is related to the borrower's responsibility, not to the money itself. You must advise your brother to avoid usurious loans and explain the harms of dealing with usury, for Allah has declared war on the usurer, and the Prophet, peace and blessings be upon him, mentioned that the consequence of usury, even if it increases, will eventually diminish.