The trick is .. to not waste your time. Status-inflicting moves, stat-raising moves, throw them out the window. You need brute force to take this crew down.
Lorelei: She's actually not that hard. If your Dragonite, assuming the team in your signature is the team you currently have, knows Thunderbolt, use that for the majority her team, save Piloswine and Jynx, which Flareon comes in handy for. You shouldn't have too much trouble with ann Electric-type attack.
Bruno: Use Flareon for his Steelix's, and Starmie's Psychic-type move, assuming you have one, for the rest of his team. He shouldn't be too much trouble.
Agatha: All of her Pokémon can taken down my Starmie if it knows a Psychic-type attack. If Nidoqueen knows Earthquake, that could come in handy aswell, although, only for Arbok, because the rest of them have the ability Levitate. For Misdreavus, just use a strong physical attack.
Lance: Again, Starmie is your best friend if it knows an Ice-type attack. Anything that attacks his team's weaknesses, which is Ice, Electric, and Rock. Meh, pick and choose for Lance.
Champion: Again, just use effective typings against him. Fearow for Heracross, Starmie for Charizard, Tyranitar, and Gyardaos? I'm not sure if he still has Gyarados, but yah. Mainly, just use types that are effective, and try not to waste time on one Pokémon, defeat them and move on.
If you're still having troubles, levelling up might be the key. You're probably just too low of a level to topple these guys, because they're really not that hard. :\