Nothing particular to it; simply read the two file sequences into separate variables and merge those as desired. It isn't clear what you actually are wanting; you talk of "two spreadsheets" in a single file but show some N combinations. That's pretty much immaterial other than keeping indices to what it is you do need at the same time or whether you're simply trying to copy all single files now into one.
Basically, all you need to know is covered in the FAQ How can I process a sequence of files? with the addition of simply using similar techniques as demonstrated there to dynamically creating file names to do similar for worksheet names.
I'd strongly suggest in this case given the type of file names you mention using the dir solution w/ appropriate wild card names to get the two groups of existing files...
