They diminish the share of the person through whom they are related. Specifically, the mother who forms their link to the deceased is reduced by their presence from one-third to one-sixth of the estate, whereas with other relatives the intermediary blocks the claimant outright.

They may inherit alongside the person through whom they are related. Thus maternal half-siblings inherit together with the very mother through whom they claim kinship, whereas other relatives—such as a grandson—do not inherit while the son is alive. Joining them in this exception are the paternal grandmother and the grandmother of the grandfather, for each traces through her son yet inherits with him. The sound principle is that an intermediary does not bar those who trace through him or her unless he actually replaces them by taking their allotted share. If he does not take that share, he does not exclude them. This is why maternal half-siblings, who do not receive the mother’s portion in her absence, are not blocked by her; and why the paternal grandmother and the grandmother of a grandfather, who likewise do not take the mother’s share, inherit on the basis of motherhood as a substitute for the deceased’s mother. Allah knows best.