Swampert: Muddy Water is an alternate to Surf - trade accuracy for a chance to lower the target's accuracy. Endeavour is a valid option for the last slot. Wouldn't go with Brick Break unless you're really paranoid about Reflect & Light Screen. Maybe Double Team or Protect (Protect goes well with Leftovers!). A sneaky option might be to have Dig instead of Earthquake if so - Dig alternated with Protect will give 2 immune turns out of 3 (depending on enemy moves used and relative speed).
Maneton: I see what you are trying to do, but you do realise this set CANNOT affect ground types (or Volt Absorb), and is going to take forever to deal with anything resistant to Electric (Electric, non-Flying or Water Grass and Dragon, plus Kecleon). It needs another attack - I'd replace Flash or Protect with something direct - the best would proably be HP Ice, but assuming you are locked in to your particular pokémon and it doesn't have it or another adequate HP, Return or Tri Attack are its best Normal options.
Hyper Beam is another possibility - if they are Paralysed on the off-turn it gives you another round of Leftovers.
Alakazam: Better off with Shell Bell over Leftovers, as are most fast sweepers with low HP and high offensive stats, but again I see what you are trying to do. Gardevoir does it better. I'm a bit wary of the mono-attack - she's useless vs Dark and Metagross, and will struggle vs other Psychics and Steel types until he has a couple of Calm Minds under his belt. She'd be better with another special attack, but her options are limited to other Psychic attacks, Shock Wave and HP-something without breeding. I'd SERIOUSLY consider training up a Gardevoir in his role or breeding on Elemental Punches.
Others seem OK. I don't see any reason they won't do well vs the Elite 4 - my comments above are mainly aimed at general play - but to be honest the E4 aren't that tough - you can beat them with pretty much any L50 team or so, and you already have legendaries on your team.