Sword characters require patience. I may actually be overthinking the match ups, though. Marth and Lucina for sure give Ness trouble. Cloud? I don't think he's as bad. All of Ness', minus his nair and dair, are faster than Cloud's aerials. Ness and Cloud have nair that comes out 5 frames, I believe. Ness' body becomes a hitbox while Cloud's sword requires a full 360 starting from his back. So you may be able to land nair before he does. Neither character has to approach, but Cloud will surely be sitting in place charging up his Limit. Your best option would be to approach him cautiously and see how he reacts. Most likely he'll either block, roll, or both. Sitting at the edge in general is a bad position for any character, and really, the only option they've got is to get off the edge, or try to get by you. Nair and uair are the two aerials to really look out for when facing off against Cloud since they're pretty good. His fair has a bit of start up time, so if he goes about doing that, then you can probably wait for it and fair him back.
His Limit creates intimidation, much like Little Mac's KO Punch. The only difference is that Little Mac's KO Punch can't be blocked and kills early. Cloud has his Finishing Touch, but I do believe that can be blocked. You may want to test that if you can. I only have a 3DS. Actually, many of his Limit attacks can be blocked. With the Limit version of his B special, it doesn't really give Cloud much time to get in and follow up. That's probably to help balance him. I don't know. I'm not sure how comfortable you are pursuing opponents while they're off stage, but with Ness, you've got the option of going out and nairing, fairing, using PK Thunder and tailwhipping his recovery, charging PK Flash and hoping it lands, or if he's close enough, grabbing him when he up B's and waiting for the grab release which will send him to his death. Spacing and baiting Cloud is key. He'll most likely do the same, but again, sword characters require patience to deal with. Cloud is tough, but I don't think he's as difficult as Marth and Lucina.
Marcina can get you off stage and counter you. Yeah, that's making it sound easy, but if they get that opportunity, they will do just that. Unlike Cloud, these two you can take a bit more time since they don't have a Limit. Many of the Marcina's I've faced will bait and punish you, so against these types, you don't want to play recklessly. Try to do the same. Throw out some attacks, do some empty hops, get close and evade. Do whatever to see how your opponent reacts and capitalize on it. So if they're blocking a lot, go for the occasional grab. If they're using side B a lot, perhaps use PK Fire. Be sure to avoid any possibility of them Countering or Dolphin Slashing out of PKF. If that becomes the case, then use PKF again, if they counter again, or follow them if they DS.