Please explain these sentence for me. i will really appreciate it.
1.A ruler had to be prepared with an heir – and often a ‘spare’as well, for good measure. What does “good measure” mean in this case. It means to have a proper measurement or to keep enough quantity?
2.The British aristocracy began as the high-ranking class of men and women who were close to the royal family, held land and castles as direct tenants of the sovereign, and played a major part in running the country. What does “direct tenant” mean? Does it mean the tenant who rent land to other tenant. Do they have the land actually? I thought tenant sometimes have hard time. Does direct tenant means lord here?

Question

Answer

2.  A tenant is one that doesn't own the land, but pays money to another (the landlord) to use the land. The British Aristocracy were direct tenants to the King, meaning the King was the only one who had authority over them in regards to their land, and they paid their rent directly into the King's treasury, not to some other person.

Answer

1. "for good measure" :  The king needed an "extra" heir, JUST IN CASE the first one died or was in some way disqualified from becoming king, then the king would still have another in line to take the throne.  Some other examples:

If I was told by me professor to write an essay that was at least 5 pages long, I might write one 6 or 7 pages long "just for good measure," just to make sure I fulfilled the requirements.

Or, if you were cooking a meal for your mother, and she enjoys it very salty. After making it salty enough, you might put in a couple extra dashes of salt "just for good measure," just to make sure it is really salty enough.

2.

Answer

"For good measure" means to be sure there is enough so you put a little extra in - like adding a bit extra rice to the pot , not just one scoop only. So the "spare " ensures that if anything happens to the heir, another son is available to inherit.
Under the feudal system the King claimed all the land and the aristocracy held their land from the Crown in return for providing service to the king and swearing an oath of loyalty. So "direct tenancy"  is the relationship between king and lord, and the king can allocate land or take it off disloyal lords. Those who lived on the land and farmed it were direct tenants of the lords.
Hope this helps you.