Unless Lucas and Ness are totally different, I can see only one of them making it in.
To me, there's two options. Give Lucas Ness' basic moveset with a few changes to make him differ from Ness a bit. Instead of PSI Magnet, his down B would be PSI Shield, which would reduce damage by half (and would allow Lucas to move), but would be broken by one or two attacks. And instead of the controllable PK Thunder, he would have PSI Teleport as a recovery. And of course, his ground and aerial A attacks would be changed a bit. Just enough to differentiate him a bit. But, for a bit of a different experience, we would include either Paula or Kumatora - a pure offensive character, wielding powerful PSI like PK Freeze, Fire, Thunder, Ground, etc. Of course, Paula/Kumatora's physical A attacks would be weaker, but I can easily imagine PSI attacks as smashes (Ground for a dsmash? Freeze for a usmash?). She would be light, but would be extremely powerful by the use of PSI - essentially Zelda if she had more magic-based moves.
The other option, which would appease both camps, is to make Lucas the PSI-based character, with Ness retaining his basic moveset. Lucas would revolve around his support PSI, like Shield, Offense/Defense Up, etc. His A attacks would be weaker than Ness', but by using PSI at the right time, he could boost his power considerably. Of course, there would be a cooldown period between uses of PSI. Basically, Lucas would be about using PSI to boost himself rather than to harm enemies.