CSV Files Open In New File Instance

I regularly process CSV files that are downloaded from various websites. The problem is, for some reason many (but NOT all) downloaded CSV files do not open in "Microsoft Office Excel" and thus, my primary workspace. They instead open in a separate instance of "Excel.exe" which is actually kinda nice because I can treat each separately, move windows around, etc. The problem is, macros that are in my primary workbook, cannot be seen by the secondary instance(s). So while I have created a number of nifty macros to clean up all the data and format it exactly how I want it in the blink of an eye, I can't run them when a file opens in its own instance.

1) How can I force ALL .csv files to open in the primary "Microsoft Office Excel" application? NOTE: Using the normal Windows Explorer "Open With..." function and setting the default application only works for LOCAL files, and does NOT work to control how remotely downloaded .csv files are opened.

2) How can I make it so that macros can be seen between Excel instances - such that when I choose to see macros in "all open workbooks", it will actually see the macros in the open workbook in the other primary Excel instance?