Okay.
Squirtle definitely gives Ness some issues. Ness can't handle Squirtle's aerial game very well... f-air helps a bit, but he just gets outmanouvered in the air. If Ness ends up in the air without his double jump Squirtle can get some juggling in... d-air and air dodge are easy to bait and punish. PKT1 is not a threat to Squirtle since he's small and it's easy to throw out a quick aerial to cancel it. As for Water Gun... it's stupid to say Ness never gets gimped by it. It's not matchup changing maybe, but it does enhance Squirtle's edgeguard game in this matchup.
Basically, if Ness is ever even slightly off the stage (out of edgegrab range) without his double jump, he is at a very high risk of getting WG'd. When I edgeguard Ness, my main goal is to get him off the stage after his double jump. Sure it's not guaranteed by any means, but when all you have to do is push him off the stage as opposed to push him far from the stage, it's a pretty scary edgeguard game Squirtle's got in this matchup. Shield the double jump f-air and hit him back out with OoS n-air. Jab combo, f-tilt, f-air, b-air, n-air all work pretty well to send Ness back out after his double jump. If Ness tries to recover from below, we can try to jump into the PKT, hit him with a b-air, or reverse WG. We can play it safer too and edgehog. If Ness goes past us, ledgehop d-air to send him back out and reset the position.
Really all I'm trying to say is that Squirtle gimping Ness should not be called "situational". It's a very real threat, and it definitely should be considered in the matchup. I do agree that the deathgrab for Squirtle, on most stages, is not as big a deal as some people make it out to be.... he doesn't have the followups that Charizard has. You cannot simply dismiss an aspect of the matchup as big as edgeguarding though. Even if you were to do so, Squirtle still has a decent advantage. I'd say 65:35 at least.
Ivysaur vs. Ness I consider about even...maybe more in Ness' favour. Bullet Seed isn't all that useful. Most of Ness' moves don't leave him open to be punished by it, and Ness is small and light. Ivy's terrible airspeed and lack of quick aerials can make him somewhat susceptible to being juggled, but I haven't had huge issues with it. Ness' f-throw near the edge is bad news for Ivy. That being said, Ivy doesn't do horribly... b-air helps a lot I find. I don't really use Ivy all that much against Ness tbh...I usually rely on the other two more. 45:55ish
Charizard... first thing that comes to mind is PKT juggling, which can be really annoying on a stage like Battlefield. Other than that Charizard does pretty well. One grab usually does mean death at higher percents (that's all I'll say about it Uffe...promise xP). He's got the range to go against Ness... Rock Smash is amazing here. Space to hit with the outermost shard and it'll be very hard for Ness to punish any of them. Short bursts of Flamethrower can't be PSI Magnet'd without prediction, and a mispredict means free grab. 60:40, but that's being kinda conservative. I think Squirtle does better than Charizard here.