All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
One has to hear from both parties regarding this issue. We cannot give a ruling by listening to one party only. So it is more appropriate for an Islaamic court to look into this matter if you are in a Muslim country or one of the Islaamic foundations if you are in a non-Muslim country. However, we can benefit you by the following:
If it is confirmed that your brothers affirm that your father donated to you this portion of the apartment, it will be either as a gift, after which your father passed away, then it becomes your property, and there is no consideration for your brothers re-iterating what they had confessed.
It could be also that it did not become your property, meaning that the flat remained as owned by your father till he died, in which case the ruling of a will applies to it; and it is legitimate for all the heirs as there is no will for a heir. The fact that your brothers kept quiet about what you did in the apartment in repairing and selling for your own benefit, is an indication that they were pleased with the donation of your father to you, which implies that the will is permissible. Thus, you are entitled to this apartment. However, we draw your attention to the following matters:
a) If we assume that you deserve this apartment: it would be a good thing if you renounce some of your rights in order to keep good relations with your kinship and to avoid disputes. You will be rewarded by Allaah if you do so.
b) What has to be taken into consideration is the current price of the second apartment.
c) What we have mentioned regarding the donation of your father to you, applies to the donation of your mother to you as well.
Allaah knows best.