It describes gods Isis, Osiris, etc. as “first royal family.” Were they historical figures?
Isis, Osiris, and related figures weren't, as far as we know, real historical figures, but figures of myth. That said, their believed relationship to real Egyptian rulers was an important aspect of these gods. All Egyptian kings were thought to become Osiris when they died, for instance. They can best be described as legendary figures: ancient Egyptians believed that they lived on earth at some point in the very distant past.
What is the term that describes the kind of pictorial writing found on these statues?
In general, the writing on the pieces you'll see in the galleries can all be referred to as Egyptian hieroglyphs or simply hieroglyphs, the writing system used in ancient Egypt.