zyzzyr said:
level 7 druid, level 7 sorcerer, level 6 sorcerer, level 6 rogue. level 7 NPC cleric.
I'm been in a long running Mystara campaign where the core party is: Illusionist/Rogue/Arcane Trickster, Sorcerer/Spellsword/Eldritch Knight, and an Enchanter. At various times there are other more melee combat characters about, but these guys are the core.
How do they handle combat?
The Enchanter usually casts plenty of summoning spells, with charms and holds to stop the enemies in their tracks.
The Arcane Trickster does plenty of buffs, and moves around to use his sneak attack. Effectively, he is a secondary melee guy who can do high damage.
The Sorcerer either blasts, or buffs and then wades into combat.
How does this relate to your group?
The Druid should be an okay tank when buffed and in wild shape. He should take the Natural Spell feat. The Druid is also good at summoning, and should be able to provide a buffer zone.
The Sorcerers will be stand back and blast guys. They need a buffer zone. They should have some summoning spells, they can help provide the buffer zone. Keep in mind that you can generate a buffer zone by spells like Fly, Wall of Stone, etc. Anything that creates a gap between you and enemy melee guys.
The Rogue should be good as a secondary combatant. He just needs to make sure he has good AC. For example, I have a Rogue who periodically helps out in the Mystara campaign. My AC is from: Darkwood Heavy Shield (+2 AC), Mithril Shirt (+4 AC), Ring of Protection, Dodge feat, Combat Expertise feat, and high Dex. It works well - I have the highest AC in the party before buffs, and I can toe-to-toe at least for a bit with the big melee guys. Longer if I have buffs like Barkskin (+4 natural armor AC, yay!), and get some healing when those HP are dwindling.
The Cleric also makes a good secondary combatant. Good armor and shield, so decent AC, and pretty good BAB. He can help provide a buffer when necessary. The Cleric is also useful for healing others in the buffer zone (e.g. summoned creatures, the Druid, and the Rogue), and for buffing those creatures. The Cleric can also summon creatures.
Spellcasting parties are going to be worst off when they can't buff. e.g. Random encounters, especially after their buffs have run out. A reasonable solution is to rest a bit more often. For encounters where they are prepared, they can be quite a bit stronger than a more melee fight oriented party.
Just my thoughts ...