How to Balance the Party with The Campaign?

[Lwaxy]

It is not as hard as you might think. It just doesn't work with pre-made adventures. In my epic, we keep getting new characters, so they and their familiars range from level 5 to level 20.

I usually manage to separate the high levels from the low levels when it is needed, and add extra encounters/adventures for the low levels as needed. For example, I get the low level Nezumi to run an errand for the high level Paladin and involve her in an encounter. Or I have the enemy target a low level to get at the head of the party.

I always build the opposing force as having different skill levels as well, so it tends to work out. Every now and then, the high levels slaughter the adversaries of low level like nothing, and at another time the low levels barely make it out of a battle against the high honchos of the other side (or even die) but all in all it is very balanced that way.

 

[Herobizkit]

1. Run a lvl 7 or 8 adventure: The paladin will have a rough time, and the ninja will probably be bored. Make sure the challenges aren't easily circumvented by the ninja's abilities, but actually require the other characters to take an active part.
2. Use the XP table in the DMG: This will reduce the XP progression of the Ninja to a crawl, while making sure the paladin will get up to speed.
3. Don't give out story awards unless you know exactly what you are doing: Sometimes you may want to estimate experience point awards for actions that normally don’t result in an XP award under the standard system. These are called story awards, and they should only be used by an experienced DM.
4. If you DO want to keep giving out XP for good roleplay, follow the advice in the DMG: XP awards for roleplaying are purely ad hoc. That is, no system exists for assigning Challenge Ratings to bits of roleplaying. The awards should be just large enough for the player to notice them, probably no more than 50 XP per character level per adventure.

Quoted for truth. This is the best advice for your situation. Given that one PC is so many levels above his peers, that player will likely be either bored or will give the other PC's an easy time catching up. Even with his higher ECL, the average ECL for the party is ~7 and the party size is nearly double the standard; adventures can probably be ramped up to 8th or 9th level and if things start to look sour, allow the PC's the option of escape.

Note that suggestion 1 will never work if you ignore 2-4.