This article says you can, but not how you do it: http://strategywiki.org/wiki/Wii_Sports/Tennis We have two remotes and tried selecting two remotes, 1 player, but that didn't do it. I know this should be fairly simple! Any ideas?
Start out with selecting 2 players, then when you get to the screeen where you can choose 1, 3, or 5 games click on the litlle people who are at the top of the screen already on the tennis court. Keep clicking on all 4 people untill you get the appropriate characters. Hope that helps.