The first thing to do is unpack the mods in separate places and then look at the contents.
If none of them have the same file names, you can just copy the lot into a single mod directory and call it what you like.
If they share the same files, then you would need to print out each version of the file, and compare what is different, then decide which change you want on each changed line and then modify that line yourself in a new version of the file. Then create a new mod using your versions.
Its not intrinsically difficult, just needs a methodical approach and some time.
