Aunt and uncle yield to grandmother and grandfather.
In my Sociology of Family class, I ask the students to raise their hands if they experienced a substantial direct relationship with a great-grandparent. As all eight of my great-grandparents predeceased me, I am surprised that so many student raise their hands. (Maybe elite college students come from families with better health and healthcare, but still.)
Demographically speaking, the decline of fertility and the increase in survival to old ages has meant that we have fewer horizontal (intragenerational) relationships and more vertical (intergenerational) relationships. And these intergenerational relationships are also more intensive, lasting years and decades.
And so, for the question of the day: Does this shift from intragenerational to intergenerational show up in the giant Google book word database? As a one-day expert in ngramology, I can conclude: Mostly, yes.
On the closest relationships, brother, sister, mother, father, the evidence is pretty good. Since 1800, occurrences of “mother” have increased from about three-times to more than four-times occurrences of “sister.”
On “father” versus “brother,” both show declines, but the ratio increased from about 1.5-to-1 to 2.5-to-1.
The picture for aunt/grandmother and uncle/grandfather is more clear. “Grandfather,” representing intergenerational, has almost completely closed the gap on “uncle,” which is one degree more horizontal:
Even more strongly, “grandmother” has vaulted past “aunt”:
You can experiment with variations here.
For an interpretation of demographic trends and aging for family relationships, consider this issue of Daedalus and a variety of recent books, some taking global perspectives, some focusing on intergenerational support challenges.