Let is a synonym of Allow. Allow is a synonym of Sanction. 
Grandparent is the opposite of Grandchild. Grandchild is the opposite of Grandfather. Grandfather is related to Family. Aunt is part of Family. 
Let <--Synonym--> Allow <--Synonym--> Sanction 
Grandparent <--Antonym--> Grandchild <--Antonym--> Grandfather <--RelatedTo--> Family <--PartOf-- Aunt 