Erm, so why did they _start training_ when i assigned them a barracks? The only thing i saw in the upper right of the 1-below-top level was an archery range, not a barracks. Standing in place with "no order" or "going to archery training" is generally caused by not having a legal barracks to train at (unreachable, no barracks assigned, or whatever is assigned actually isn't a barracks).
Edit: you could also deactivate them, which would remove the "can't train because of no barracks" lock. You'd still need to completely re-organise the equipment so they have matching weapons and ammo. Your archers are never going to shoot if they wield javelin launchers but have bolts in their quivers. To do this, you'd have to edit the uniforms to use e.g. only "crossbows" or only javelin launchers instead of "ranged, individual choice". To ease their self-management, you could also remove all inappropriate ammo from the ammo assignment screen. I'm not sure, but they might _claim_ inappropriate ammo without ever picking it up, thus blocking its use for other squads.
I think as long as you specify a specific weapon type (crossbow, bow, launcher etc.) and matching ammo, they should at least be useful in battle, but you seem to be making progress getting their training issues sorted out, too.
@below: hmm, can it be beds work differently from armour/weapon stands or cabinets when used as barracks? Or was the bed not set for training? - that'd break them, because ime active training, including archery, _has_ to begin with an "organise training" session in a _barracks_. It's totally possible that there are some weird effects i've not seen yet, though. I guess i'll take another look at beds and the additional squad assignment flags next time.