My brother and I are making a video for YouTube, and since we need four voices, and only have two people, we made two separate WAVE Audio Files that are each seven seconds long. I need a way to combine the two so that the sound from both comes from one audio file. How can I do this?

I'm not the expert here but I think, depending on what end result you're after, mixing might be the answer to your problem. Mixcraft supports WAV files. You should be able to open both files at the same time with this program and mix them together. It is a shareware application but most are free to try for 30 days so you can probably download it, try it and if it does the job you'll have done it for free.

Your other option is an editing program such as audacity which has the added bonus of being freeware and it does state that you can "mix sounds together" and it too supports WAV files.

Sounds like you`re trying basic multi-tracking. Try Audacity (free) or Kristal (also free). I use Kristal all the time for basic stuff up to 8 tracks. Either of these should do what you want.
modo