Is the questioner entitled not to relinquish his right to the house, and to his brother's residence in the apartment, knowing that the father refuses this and wants to seize the apartment for the coming newborn?

If you undertook to build your father's house with the intention of claiming the money back from him, then you have the right to demand the expenses from him. As for the apartment you built above your father's house at his insistence, it appears that he gifted you the upper part of his house for you to build on it, and the apartment is yours, and you have the right to sell it. Your father has the choice between buying it or letting you sell it to your brother. It is best that you discuss this with your father wisely or through an intermediary who can reconcile between you. If you leave all of this to your father, it is better, and Allah will compensate you with good.