Don't let a low-tier character tell you that the matches are going to give you negative results. My brother uses a low-tier and we got forth out of about thirty players in an online doubles tournament. Sure, it was online, but still, we did a lot better than we had expected. Ness and Lucas don't have the same bad match-ups, they have similar ones. Both characters have subtle differences in abilities, don't play the same in playstyle, and they also have the same good counterpicks. Take your weaknesses and make them your strengths. A bit of advice for a Ness main. If your team is taken to a stage such as Yoshi's Island, Ness can use the ShyGuy's as firewood by setting them on fire.
Anyway, with Ness and Lucas, it's obvious what both characters can do to help each other out. For health, you've got PK Flash/Freeze, Fire, and Thunder. If Lucas is knocked off the stage with no recovery, Ness can use his PK Thunder to hit Lucas to bring him back. Ness has good KO potential, and Lucas has good set-ups for killing. If you and your teammate know how each other work, then you shouldn't have a problem getting far with Ness and Lucas. Don't let the idea of a stupid match-up get in the way of your mindset, or you won't see yourself getting far.