1. Assuming that the landlord died intestate ( without executing a WILL ), the share in the property devolves equally to his wife ( if alive ), three sons and three daughters in the share of 1/7th each.
2. Daughters are also treated as Coparceners on par with Sons, as per Amendment to the Hindu Succession Act, 1956 in 2005 and subsequent judgements in this regard which is retroactive, with certain conditions.
3. Based on above, the three daughters are entitled to equal share on par with their three brothers in their deceased father's property.
4. Since you had bought this property and invested your money to get the property converted to non-agricultural status, send a legal notice to your seller/s who sold the property to you, to get back your investment OR convince the three daughters to come to a compromise and withdraw the case, so that you can pay some compensation to them, so that you can retain your property.