The property in the name of your grandfather automatically devolved on the legal heirs of his deceased son.
Therefore your brother who had been enjoying the property cannot claim the entire property as his own property, it devolves equally on all the legal heirs of your deceased father, which includes your mother also.
If he is claiming the entire property, you may file a partition suit and separate possession of your legitimate share in it.
The settlement deed drawn on the lines of mutually agreed conditions which includes allotment of a share to your mother is very much valid.
The registered settlement deed executed by your mother in favor of her sons in respect of her share in the property cannot be revoked at this stage
If the brothers quarrel for allotment of property share and its location, you may aproach the court of law for a proper partition.