The Hittites indeed suffered heavily from civil war in the 13th century BCE, and the effects seem to have been felt for a century or more. The Hittite royal household was always inordinately fond of conspiracies, assassinations, and coups, however, and extended periods of peace are quite rare in Hittite history.

It's doubtful one can assign much, if any, blame on the Sea Peoples for the collapse of the Hittite empire - which should be distinguished from Hittite civilization. For one, the Hittite empire was virtually always a landlocked empire with little access to or interest in the Mediterranean Sea or Black Sea. For another, the Hittites had their hands full with other belligerent groups, including the Kaška peoples in the north, the rebellious Arzawa lands in the west, recalcitrant vassal states like Išuwa in the south, and the ever looming threat of Assyria, a rising power in the 13th century BCE. To this mix, one can add other groups like the Aramaeans and Phrygians, who rose to power in the Iron Age and shook up the geopolitical landscape of the ancient Near East.

There is always more to be said on the end of the Hittite empire, but I wrote about it in How did the civilizations fall in the end of the Bronze Age?

The relationship between the Neo-Hittite (or Syro-Hittite) kingdoms in Anatolia and northern Syria and the biblical Hittites is still poorly understood. Some scholars think the two are wholly unrelated, some think they are one and the same, and still others think they are only loosely connected. I wrote more about this in this post.