Short answers, pulled from the story.
The three elderly men are Cleinias of Knossos, Megillus of Sparta, and an Athenian Stranger. They walk along a path on Crete discussing the nature of law without Socrates appearing in the text.
Plato wrote The Laws as his last and longest dialogue during his later years when he may have felt his political efforts had failed. Scholars suggest this shift in tone reflects his attempts to guide Dionysius II of Syracuse.
The entire narrative unfolds during a single day-long journey between two sacred sites on Crete. The group walks from Knossos toward the cave of Zeus on Mount Ida where Minos supposedly received instructions every nine years.
Book X presents Plato's argument that soul exists before physical matter in both explanation and reality. He refutes earlier philosophers who claimed corporeal things like earth and fire came first by arguing that soul is intelligent and self-moving while supervising the entire cosmos.
The city of Magnesia permits private property and family units unlike the ideal state without written laws found in the Republic. Guardians in the Republic live communally without families but Magnesia preserves traditional households and relies on written law.