Having a well balanced team with pokemon that cover the weaknesses of others will help a lot. Also, it's crucial to use attacks that are super effective unless your pokemon are crazily over-leveled. I finished the kanto elite four with the team in the imgur link below.
imgur.com/a/HRtkO
For Lorelei, I used Magnezone's and Gengar's Thunderbolts. When she sent out Jynx, Flash Cannon did the job.
Bruno was pretty easy with my Golduck. Surf for Onix, then Psychic for his fighting pokemon. When Golduck fainted, I sent out Crobat for Acrobatics.
Agatha required Magnezone to paralyze Mega Gengar. After being crippled by paralysis, it would not be able to attack first. Gengar then used Shadow Ball -> got one shot -> revive -> Shadow Ball again.
Magnezone dealt with Lance's Gyarados easily. Granbull's Outrage was able to two-hit Dragonite. Aerodactyl was a bit tougher since I wasn't able to outspeed him.
Finally for Blue, attack with type weaknesses and make sure to paralyze Alakazam.
As you can see, both my Magnezone and Golem have Sturdy. This ability is very helpful since you can basically revive your other pokemon during the two turns they are out. I did train my main attackers in full speed and attack / special attack so they would be able to one-hit most of the elite four.
To see the full roster of each elite four member's pokemon and the order they are sent out, this post is very useful: pokemonrevolution.net/Forum/viewtopic.php?t=8077
As for your team, an Alakazam would fit in very well. You could even use two level 14 magnemites since you'd only have four pokemon for Sturdy fodder. The benefit of using magnemite is that if you send it out after one of your pokemon faints, you can use Thunder Wave to paralyze the opposing pokemon and then use a revive on one of your attackers to finish it off. My last suggestion is to carry a lot of revives and hyper potions.
Good luck, and hope to see you in Johto soon!