1. Since, on record, your father was the joint owner of the property with you, on his demise, as per his WILL 50% of his share in the property would devolve to your brother and the other 50% of your father's property would devolve on you.
2. The registration of WILL is optional and a non-registered WILL with 2 witnesses is legally valid.
3. In the joint ownership of the property if one person dies, then the property would devolve to the surviving owner and the legal heirs of the deceased owner. In the instant case, your ownership of 50% share + 25% as one of the legal heirs in the property of your father would devolve to you. Other 25% in your father's share totalling to 50% in the entire property shall be shared by your brother.
4. Convince your brother of the reality that you are the one who invested 100% of hard earned money while buying the property with your father and there was absolutely nil investment from your father at the time of buying the property and negotiate with your brother to achieve into mutually agreed terms.