My tip is to start with 8 in their primary attribute and then go for speed and con. Exeption for archer which could do with some perception as well. Abstain from picking a talent at lv 3 and go for glass cannon when you reach lv 5. If you can train your tactical ability to avoid taking damage, you'll be able to reach 20 ap quite early.
Cain is the best melee henchman with 10 more skillpoints than your starting characters at lv1.
Zalazzar is a better mage than Jahan, with 3 more skillpoints at lv1. He can also be made into an Aero/geo mage so you can have a starting mage with pyro/hydro. This gives better team synergy because you'll be able to cooperate your two mages to do the same combos together instead of different combos apart. This way you can avoid having your mages tripping all over each other with one freezing the enemy only to have the other thawn him with fire.
When you reach level 6 you should swap zalazzar for Elessa, the very best henchman in the game, with 15 more skillpoints than your starting characters at the same lv.
Give all your characters 1 level in each magic skill and marksman. Give all characters summon spider, tactical retreat, teleport, minor heal and other usefull spells you don't need high int for. Give all characters all summons once you reach the relevant levels. You can cast summon with all before you enter combat, making the extra ap-cost for low skill-level irrelevant.
Consider giving your archer and melee char a point of sneak and gurilla for the midgame. You'll need to be able to reach sneak 5 with them through equipment for it to shine tho.
Have fun
Edit: Also remember that you don't have to start the game with marksman skills for your archer. She'll have a much stronger start with summon spider, teleport and walk in shadows. You mage will have a strong start with summon spider, headvise and minor heal.
