nesting jarfiles isn't supported.
There are some proposals to allow for it, but nothing has yet reached prototype stage.
So at current the only way would indeed be to unpack the jars into one folder and repack them as a single archive.
Better (usually) to just add them all separately to your classpath.
It's a very rare case where there is a need to repack jars, usually it's only applicable when deploying packages to an application server where they would interfere with older versions of those same packages that the application server needs internally, a situation rare enough that most people never encounter it (I myself only have seen it once so far in a decade of using Java professionally).
I found that packing a jar in other jar is possible(like any other file), but using the packages inside the jar is not possible.
The only way is to unpack the jar, & repack the classes of it in final jar file.
There is no DOS command for unzipping jar files as DOS doesn't have a built-in system for interpreting the file format.
Maybe some DOS program can read and interpret the files (they're just ZIP files after all) but not DOS itself.
And you're certainly not going to run Java on DOS as Java has requirements that DOS never met.