Why did Yoktan merit having so many children?
Rashi: Because he made himself small, as his name suggests. 1
Perhaps this is another indication of Eiver's power of prophecy. See Radak for an alternate explanation of Yoktan's name.
Why did Yoktan call one of his sons "Chatzarmaves" (lit. "the courtyard of death")?
Rashi: He named him after the location where he lived. The Midrash explains that, due to dire poverty, they would eat hay, 1 wear reed-clothes and await death always.
In fact, the commentaries explain that it was called "Chatzar" on account of the Chatzir (hay).
רש"י: חצרמות - על שם מקומו: למה נקרא המקום כך?
גור אריה: כתוב במדרש שהיו רגילים למות שם בכל יום.