Rights of legal heir in the ancestral property

My grand mother's (my mother's aunt and she is her foster daugher)having 2 elder sisters as unmarried and 3 younger brothers, out of this 1 unmarried. Only 1st brother having 2 male 1 female(my mother) issues. My g.m.'s elder sister gifted her properties share 1.to her 2nd brother a conditional gift as life interest only, if he is having no issues the property returns to her and her heirs 2. To my mother 3. To her 1st nephew's 3rd son 4.2nd nephew's 1st son with full rights. Now the issue is the 1st share holder's property, he and his wife died without issues, as per the will condition the property returns to my g.m.'s elder sister. Now who will be the legal heirs to this share, and what will be the share part to my mother.