As you mother has died intestate your father is share holder in her property.
Since your father has children form other wife they can cliam the share of thrie father.
As you state that he is not intrested in the property in question , then if you need to pay any lump sum to you father pay him and get him released from his share.
EIther he should gift the property to you by executing a registered Gift deed or he should execute a registerd relinquishment deed.
Though the property is still in your mother's name he cannot mortgate or raise a loan until the property is not transferred to him as per his share.
If you desiere to transfer the property it shall be legally transferred in three share holders .