You can get away with Scald>Surf on Swampert if you decide to run a more defensive spread on it. Those usually run something like Stealth Rock / Earthquake / Scald / Toxic\Roar. That allows them to work as a decent support which is especially nice for your Scizor, as Swampert can take care of Fire types.
On Scizor run U-turn/Bug Bite over X-Scissor. Bug Bite is stronger and U-turn gives you momentum and helps you retrieving one of your setup mons.
HP Fire on Jolteon is not that great. If you wanna go for Jolteon either HP Ice or Grass is a good option. Or, I suppose, if it's not possible, then just run Shadow Ball.
Dunno about Gallade. It's pretty slow, doesn't have many good resistances and can't take that many hits. I guess Shadow Sneak is also an option, but sadly it just doesn't really deal much damage.
If you decide to play without items, then picking mons that can get around not having an item is a good strategy. That includes mons with Adaptability like Dragalge and Crawdaunt, or Magic Guard on Clefable and Reuniclus, or if you wanna go more defensively Regenerator mons like Amoonguss and Slowbro. Intimidate users are pretty good, because they reduce opposing physical damage even more, allowing you to take even more hits. In general: without attack boosting items, it's a little harder to deal a lot of damage without a setup beforehand, so your setup mons (e.g. SD Scizor) should be used more carefully.
Also, since there's no item Knock Off is never going to get its boost, so whenever you have a choice between Knock Off and Night Slash, you should pick the latter. It not only deals more damage period, it also has an increased critical hit rate, helping mitigate the lack of an item. Just keep in mind that criticals are hax, so don't rely on them too much.