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, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
If the house which you mentioned in the question is owned by your father and your uncle is trying to acquire it without right, then he is very wrong and he is indulging in transgression, injustice and severing ties of kinship.
However, among helping one’s Muslim brother when being an oppressor is to prevent him from oppression. Anas narrated that the Prophet, sallallaahu ‘alayhi wa sallam, said: ''Support your brother whether he is the oppressor or the oppressed.” They said: “O, Prophet of Allaah: It is all right to support him if he is oppressed, but what about supporting him if he is an oppressor?” Thereupon, the Prophet, sallallaahu ‘alayhi wa sallam, said: ''By stopping him, i.e. by preventing him from being an oppressor." [Al-Bukhari]
Hence, we advise you first of all to supplicate Allaah to guide your uncle to the straight path, and also to seek the help of some rational and wise people who might influence him to advise him and try to make him regain his senses and reason, as this is the best manner of being kind to blood relatives.
If he stops his transgression, then praise be to Allaah, otherwise one may look at the following three options:
1- Trying to reconcile with him by giving him some money, for instance, in order to avoid his evil, repel his plots and preserve the affection and ties of kinship with him.
2- Taking the case to an Islamic court so that they would stop his transgression.
3- Leaving the matter in the Hands of Allaah (i.e. being patient with your uncle until Allaah judges between you and him).
Allaah Knows best.