to do this you need one itunes library. I understand you have two iPods are they both syncing with hte same itunes library. If so just sync the all content onto one iPod if you have enough space. Some peope have a lot of music and video.
If you have two itunes libraries that you sync each ipod with then you need to merge them these are your options if itunes are on separate computers
If they are on the same computer but different logons then copy the music foler from one account to the other.
Once everything is in the same iTunes you may also need to Authorise the computer with the other persons Apple ID
Then you should be good to go