Do these fittings have sealing washers or ferrules included?

The fittings come ready to thread in. Check your turbo or supercharger manual for any specific washer or ferrule requirements—some chargers need them, some don't.

Can I use this line for both feed and return, or just one direction?

This is a feed line kit. Use it for oil going into your turbo or charger. Return lines typically have different sizing and routing, so get a dedicated return line for that circuit.

What prep work do I need before installing?

Clean your block and reservoir ports before threading in the fittings—debris in oil lines kills chargers fast. Thread by hand first to avoid cross-threading, then snug with a wrench. Don't over-tighten.