Is it permissible to seize an apartment from a deceased brother's inheritance as compensation for a previous right that he did not fulfill, even though the value of the apartment is greater than the original right, and the heirs refused to accept a settlement by taking only the right and relinquishing the apartment?

If your brother reneges on what was agreed upon and withholds your right, then proceed to sell the apartment and accurately take your right from its price. This is not consuming the orphan's property, but rather obtaining a right and absolving your brother of his responsibility. Whatever remains of the apartment's price, pay it to his heirs.