Catan pirates and explorers ships and roads
Yes, 2 ships and a road can share a coastline.
According to the FAQ for Catan Pirates and Explorers:

Sea Routes - Are only ships allowed on &quot;sea routes&quot; located between
terrain hexes and sea hexes / frame, or may I also build roads there?
Roads may be built on all paths, both inland and along the coast. At
the shore, roads can be parallel to ships, meaning that up to 1 road +
2 ships may simultaneously occupy a path on the coast.

Source :
Catan FAQ page 157