What species did sharks and turtles evolve from? They have been around for Millions of years with little change. If each species we have?

We still do not know the direct ancestor of turtles, because the only known fossils already had shells. It is likely that they evolved from a anapsid reptile, which is a kind of reptile that does not have any temporal openings in the skull. Anapsid reptiles are the earliest known kind of reptiles to have evolved from an amphibian. Other reptiles, such as lizards, snakes, crocodiles and the reptilian ancestor of mammals and birds all have temporal openings in the skull. Some scientists claim that the ancestor of turtles have temporal openings in their skull too but those openings have since been closed. The problem with that is that even the oldest known turtle fossils lack any sign that their skulls had openings or even signs of a opening that was later closed.

Currently sharks are thought to be the descendants of a group of extinct ancient fish known as spiny sharks, scientifically known as acanthodians. The acanthodians are also thought to be the ancestor of bony fishes.

Some ancestors of modern sharks appeared 450 million years ago, but "modern" sharks have existed only about half that time. Yes, modern sharks evolved from earlier species, but as you said, many of the present-day sharks are not much changed from those of the Cretaceous era.

There are some disputes about the ancestry of modern-day turtles. See, for example, Rieppel & Reisz (1999), in Annual Review of Ecology & Systematics.