If Devin is 12 years old, then Eden is 2 * 12 years = 24 years old.
Since Eden's mom two times older than Eden, her age is 24 years * 2 = <<24*2=48>>48 years.
In total, they have 48 years + 24 years + 12 years = <<48+24+12=84>>84 years
The average age for the three is 84 years / 3 people = <<84/3=28>>28 years/person
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