North and Hillard 87.2

87.2
He was descended from kings, but he did not enjoy kingly power himself.

I translated this (awkward) sentence thus:

Regibus erat prognatus, sed ipse regnum non fruebatur.

Does fruor take an ablative always?

Regibus erat prognatus, sed ipse regnum non fruebatur.

it should be est prognatus, for erat prognatus is plusquamperfectum; and regno fruebatur, for regnum is accusative.

Does fruor take an ablative always?

yes, always: aliquis aliquo fruitur