Ether nomenclature: Oxygens on alkyls and alkyls on alkyls
Names for ethers can be formed by five different methods. Furthermore, various traditional names are retained for use in general nomenclature.

According to the current version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book), preferred IUPAC names of ethers $\ce{R-O-R'}$, when $\ce{R}$ and $\ce{R'}$ are both aliphatic groups, are formed by substitutive nomenclature. In substitutive nomenclature, when $\ce{R}$ is different from $\ce{R'}$, $\ce{RH}$ is chosen as parent hydride and $\ce{R'-O-{}}$ is cited as a substituent to it.


  P-63.2.2.1.1 Substituent prefix names for $\ce{R'-O-{}}$ groups are formed by concatenation, i.e., by adding the prefix ‘oxy’ to the substituent prefix name for the group $\ce{R'}$. (…)


For the first example in the question, the name of the parent hydride $\ce{RH}$ is ‘decane’.
The substituent prefix name for the group $\ce{R'-{}}$ is ‘2-ethylheptyl’.
Thus, the substituent prefix names for the $\ce{R'-O-{}}$ group is ‘(2-ethylheptyl)oxy’.
Therefore, the preferred IUPAC name of the compound is ‘4-[(2-ethylheptyl)oxy]decane’.



For the second example in the question, the name of the parent hydride $\ce{RH}$ is ‘decane’.
The substituent prefix name for the group $\ce{R'-{}}$ is ‘3-propyloctan-2-yl’.
Thus, the substituent prefix names for the $\ce{R'-O-{}}$ group is ‘(3-propyloctan-2-yl)oxy’.
Therefore, the preferred IUPAC name of the compound is ‘4-[(3-propyloctan-2-yl)oxy]decane’.