Hello there, in order to answer your question (by me or other historic fans/experts), I'd need to have some specifications.

The Middle-Age era cover a huge portion of History (V-XV century, so 10 centuries), and England is very peculiar by the fact it is not on the continent and wasn't united until late. Furthermore, each country has its own nobility rules, so you end up with nobility rules for the Jutes, the Saxons, the Angles, the Normands, the Brit (in here, Brit as in the Welsh, the brittons of England pre-invasion)....
For example, in most of the Anglo-Saxons kingdoms the nobility titles were more a reward (earned) rather than something hereditary. You even had your title for your life time and then the family would lose it. The rules for getting it was also pretty chaotic in the early ages the primogeniture rule wasn't the common way ; usually it would go to any noble who claimed it, then more toward the ruling family but not exclusive to it. In comparison, the Normands apply a more feudalistic system were the primogeniture or salic sharing (sharing the titles among the kids/family or the ruler at his death) is more common.
Another important point : each title can have its own rules, especially with viscounts were it's more an administrative title linked to nobility rather than a noble title itself. And again, that concept of feudalism wasn't really a thing in England before the Normand came and changed everything. In Normandy itself viscounties even disappeared in a way because the counts took their power away.

So, it depends on :

- the time frame you're talking about
- the country
- the culture