Are all of these neighbouring places on friendly terms?
--There are so many of them, so close together without much in the way of buffer zones. I just wonder if things would be a bit hairy with them so closely packed together.
The short answer is no they are not all on friendly terms.
First the area controlled by the Tharian Overlord of City-State is a confederation. The Tharian Horselords of Laknost, Bernost, and Gaenost along with the Elessarians of Halnost, and the Ghinorian of Dearthmead have created a Senate which elects the Overlord of Tharia and the City-State. The Overlord in turns adjudicates any disputes between the members of the confederation. The Senate adjudicates any disputes between the members of the confederation and the Overlord. This was formed over a hundred years ago to resist the expansion of the Third Empire of Viridistan.
The dozen Tharian Coast kept their freedom from City State with the aid of Sotur and the Pokrantril League (off-map to the north). At first Bernost was part of the Tharian Coast but in the conflict that led to their freedom Bernost was conquered by the Tharian Overlord. In the hundred since the Dukes of Bernost have gone native and now plot rebellion to join the Tharian Coast.
The Duchy of Halnar joined the confederation several decades ago when the Kingdom of Antil was in the midst of a civil war. Their faction was one of those who lost to the present dynasty of Antil and so sought the protection of the Tharian Overlord.
Bulwark, the City-State and the Marches are the personal territories of the Overlord. The Marches were conquered by the Overlord using his personal resources. In the early days of the confederation the resources of the duchies overshadowed the Overlord's resources. But in the present the Overlord commands equal strength to that of the combined forces of the duchies.
The Northern March was the result of an alliance between the Overlords and Thunderhold. The region between City-State and Thunderhold was cleared of orcs and monsters. The Dwarves took the northern part of the territory and the southern part became the Northern March. Likewise the Eastern and Southern Marches was cleared of Orcs and Monsters. The March of Dearthwood is the latest project of the Overlord formed to coordinate the destruction of the orcs and monsters of Dearthwood. The Palen March was created at the same time the Duchy of Halnost joined the confederation. The Overlord of the time took the east coast of the Romaillion Sea away the Kingdom of Antil. Seizing everything down to Palen Springs.
Bulwark is the ancestral clan home of the Tharian Overlords and was their personal territory since the beginning of the confederation.
Thunderhold is an ally of the Overlord and the Confederation. They are entitled to send a senator to the Confederation Senate.
Warwick was founded by Pirates. It is a melting pot of Skandians, Tharians, and Ghinorians. It is despised by all the surrounding realms. Only the fact that those realms have conflicts of their own kept them from destroying Warwick. It is also noted for it open worship of the dark gods, Set, Kalis, and Hamakhis.
Croy is a Skandian Viking Kingdom noted for it's Scholar and religious shrines. It is wealthy and can maintain a large navy for it size.
Loshain is the refuge of the elves who survived the fall of Silverwood, not Dearthwood, 400 years ago.
Limerick Shire is a halfling realm. Once the breadbasket of an alliance of demi-human and human realms it is a now refuge that barely maintains it's borders.
The Principality of Modron is a Ghinorian Colony that struggles to weather the Viking raids of the Skandians.
The Kingdom of Lightelf is a gnome realm. They are are ashamed of their actions during downfall of the demi-alliance and now do whatever they can to assist the surviving realms.
Like Modron, the Kingdom of Nomar is a ghinorian colony. Here the Skanadian have estabilshed the Kingdom of Ossary and the two kingdoms are in a long twilight struggle to see who will survive.
The Halkmenan Empire is loose alliance of Sarnic City-State devoted to the worship of the Dark God Hamakhis in his aspect as Judge of the Dead. They are in the midst of a war with City-State as Divolic, Warden of the Southern March conquers the city-states one by one.
Onhir is another refuge of elves that survived the fall of Silverwood.
The rest of the details including some of the history is in my Majestic Wilderlands.
On Monday I will have a follow on post explain why I think all this works plausibly.