Property

I and my parents staying in 2 bedrooms flat for 15 years and this flat is on a notary in my father’s name. This is the notary agreement made between my father and his elder brother. My father's elder brother was NRI and after he retired, he came back to India and start staying on the ground floor which is his own house. After coming back to India his intention was changed and start harassing my family and we thought to move out to some other house on a rent basis. After we have moved from our flat, my father's elder brother broke the lock of the house and took possession of the house and told us that this house is no more with us. Now the relationship between my father and his elder brother becomes worst and now my father's elder brother changes his mind and tells that there was no notary or legal document made between them. We have all legal documents like a notary and my father also showing this flat property in his income tax return. Please let us know how to retrieve this property in legal