Amount received from brothers in lieu of relinquishing right to property


My grandfather’s (mother’s father who passed away several years as is my grand mother) property (65 yr old) is being sold. My mother has three brothers and a sister. The brothers are ready to part with an amount which is only a fraction of the share rightfully (1/5 of the selling price) due to the sisters, for which they have agreed. However, the sisters would want to execute a relinquishing deed to give away their right to the property in lieu of the sum offered by the brothers. Now, is the sum being offered by the brothers (if cheque is in their name) subject to CGT or it can be treated as gift.