You need to check with your brother to see whether he is planning to pay any tax due on any gain that needs to be reported from the sale.
Otherwise, if your brother received 100% of the proceeds from the sale, deposited those proceeds in his account, and then gave you a share, he essentially gave you a gift.
The recipient of a gift (the donee) does not need to report the gift on any tax return. The person who gives the gift (the donor) may have to file a gift tax return.
