Whenever you look at a specific relationship in DNA terms, there is a range of cM associated with it. The cM range for any given relationship will overlap with, usually, multiple other possible relationships.
We all start with 6800 cM. If you compare yourself to a test of yourself, or your identical twin, it will be more or less 6800 cm. You and your child will have a match of around 3400 cM. After that, it can get dicey.
Your child has approximately half her/his DNA from you and half from her/his father. But that half that is from you...how much is from your mom and how much from your dad? The average will be 25% each. Meaning everything divides neatly in half. But the reality is always a range. There's no way to predict which side of any given DNA strand will be the one passed down to a child.
Eli and Henry Jr. are first cousins and they share a single set of grandparents. In theory, they should each have 25% of their DNA from each of those shared grandparents. This means around 1700 cM inherited from any given grandparent (numbers are rounded). In reality, the range of cM from each grandparent is 1156-2311 cM. Add to that the fact that each grandchild will inherit different DNA segments from each grandparent, not just different amounts of total cM.
Eli's first cousin once removed, Kevin, may have, as PolyGeo points out, nearly all of the DNA his dad had from one or more of his paternal grandparents. Or he may have inherited very little.
Both Eli and Kevin will be within the cM ranges for the relationship they have with you. Use this information to narrow down what relationship you have to this family. Because of the disparate numbers, you have an opportunity to narrow down the possibilities more than most people do.
There are also other explanations.
You might match Kevin through both his mother and his father. This is not uncommon in general but, if you all belong to an endogamous ethnic group (any group that tends to marry people of that group, even if they are not known family, for example, Jews, Hawaiians, Mennonites, Colonial Americans, etc), then it's more common to match over multiple lines than just one line.
It is also possible that Eli's and Kevin's family has some secrets, but that is not the conclusion I would jump to. Everything you describe is perfectly normal and easy to explain.