Is it proper to use plurals when the subjects are actually singular Example A picture book story about complicated daddies wicked stepmothers and daughters who learn to be brave in the dark woods?

No. If there is only one daddy and one stepmother and one daughter then you don't write the Word as plural. Daddies means more than one daddy.

If the characters are singular then you need to have 'a' before complicated/wicked/daughter.

A picture book story about a complicated daddy, awicked stepmother and a daughter, who learn to be brave in the dark woods.