we have not registered the relinquishment deed into mothers name. so if the deed is not registered then cant she made the WILL favoring one of her child
A registered release deed relinquishing the rights in her favor shall be a valid document to confer the marketable tittle to her without which this can be disputed by anyone at a later stage because unregistered document is not valid in the eyes of law.
As we dont have enough money to register the Relinquishment deed so how can she get rid of her that son so that neither he can claim on her property neither he raise any objection in court in future.
Legally you cannot get rid of him due to yor own difference of opinion with him.
He is a legal heir of your decesed father hence you cannot deprive his rights in the property at your own whims and fancies.
If the relinquishment deed is not registered then the danger of he emerging with his rights in the property at a later stage will be imminent and there can be serious question about the validity of marketable title to your mother in the entire property, hence her will also cannot be maintainable in law.
Better do not risk the issue, you can get the problems solved legally now or never you can live peacefully with the sword of Damocles hanging on your head for ever.