Will the brother who sold his brother's house without his knowledge and consent be held accountable on the Day of Resurrection, or are full siblings not held accountable to each other like parents?

It is not permissible for a brother to dispose of his brother's property by selling or otherwise without his permission. His action is void unless the owner approves it and consents to it. This action is called "unauthorized disposition" (tasarruf al-fuduli). Scholars have differed on the ruling regarding the sale by an unauthorized person. Some view its validity as contingent upon the owner's ratification, while others believe it is not valid at all. Those who permit it have differed on whether it is permissible to initiate such an action or not. Its permissibility is restricted by benefit; if there is no benefit for the owner, it is unlawful, unless it is out of fear of the property's damage or loss, in which case it may be permissible or recommended. The one who commits an unlawful act will be held accountable for it on the Day of Judgment. Therefore, the brother should be forgiven for what he did, out of consideration for the bond of brotherhood.