Typically speaking, landed titles (straight-forwardly) could go Baron -> Count/Earl -> Duke -> King -> Emperor, with some titles having leeway to squeeze between. A couple such titles would include Margrave/Markgraf/Marcher Lords (common in the Holy Roman Empire and England) and Grand Duke (common in Italy and the Slavic realms).

As the hierarchy generally goes, there are multiple Baronies in a County/Earldom, multiple Counties/Earldoms in a Duchy, multiple Duchies in a Kingdom, and multiple Kingdoms in an Empire. However, sometimes there could be Counts/Earls directly reporting to Kings (Anglo-Saxon England being an example) and Dukes reporting to Emperors (the Holy Roman Empire being an example).

Margraves/Markgrafs/Marcher Lords are typically people who hold multiple county titles but are for some reason or another not Dukes; they are usually given this much authority by the sovereign of the realm for the purpose of defending a border and the resources such a task would require. Examples of this are the Spanish March in Francia under Charlemagne, the Welsh Marches in England, and the numerous titles named Ostmark (Eastern March) in the Holy Roman Empire, some being Saxon, others Austrian.

Grand Dukes, similarly, are those who hold multiple Duchy titles, though this is usually as a means of asserting their independence and sovereignty as opposed to being sworn to a King. There were numerous Grand Duchies in the high middle ages and these usually were under great pressure to be a part of neighboring kingdoms, but these conglomerated titles instead were powerful enough to be realms in their own right, even if their sovereign wasn't officially a King.

The answer to the first question is complicated. The answer to the second question is no. Medieval fiefs can be thought of as having a grantor and a grantee, but that is about as concrete and straight-forward and linear as it gets. For example, as far as rank goes, you could theoretically have a person who is both the King of England and Duke of Normandy. That person, as the Duke of Normandy, might owe allegiance to the King of France; but as the King of England, that same person might have a claim on the kingship of France. The best book I have read on the topic of fiefs is "Fiefs and Vassals". The main point is that there were standard practices and types of fiefs within a particular region, but that each fief was unique and each relationship between grantor and grantee was unique. As far as medieval titles go, that was more-or-less linear in terms of which title was "higher" than another within a particular geographical area. Serfs were always of lower status than knights, which were of lower status than titled nobility (although those titled nobles were frequently knights), and so forth. Kings were almost always on top (excepting the odd "Emperor"), But you could have an independent duke who answered to no king who was more powerful than a king of a small country.