Just to make sure we are on the same page, I assume you are using this list: right here?
Legally, there is no reason you can't do both. You can arm them with spears and halberds and shields and just use whichever weapon is the better for the situation. Sword and shield is also a very defensive combination good for survivability. Of curiosity, are you using the house-rule that lets shields adds +1 to armor saves in melee? It is one my group has been using and I can definitely recommend it for helping reduce dual-wielding. What dual-wielding house rules are you using?
Also, consider having at least one person armed with a DHW and either spear or sword. The DHW will be handy for charging knocked down opponents.
Personally, I would lean to spears and swords for the leader and shaman because defensibility is paramount for them (the leader because he is irreplaceable, the shaman because he cannot wear armor) and spears and halberds for the Braves, except for 1 or 2 braves that have a DHW instead of a halberd.
For starting weapons I would probably go spears over anything else just because they are 5 gold instead of 10 gold, so get them now and any secondary weapons after the second game. Pity you can't *start* with ithilmar weapons
That poison looks fantastic (+1 to the injury
roll? That doesn't go away? Yes, please). Poison as many weapons as you can, over time.
In my group we have house-ruled Ithilmar armor to be a kind of light armor. This may or may not be acceptable to your group
Just by-the-by, do you have any idea what the special goblin skills are? The braves seem to have access to them, but I can't find what they actually are.
Disclaimer: I have never played with or against Forest Goblins, so this is all theoryheim. YMMV. A lot.