I've just installed Dawnguard and have been having trouble with the crossbows. After following some of the advice in [this]([Dawnguard DLC] Crossbow Questions ? - The Nexus Forums) thread, I've been able to get the crossbow to work for myself, usually. Sometimes I'll have to equip it, un-equip it, then re-equip it for it to work right. However I cannot use the crossbow in third person (no big deal really) or while sneaking. Every time I've tried to fire it while sneaking it will jump to an animation scene, but instead of firing in slow-mo, all my character does is stand there. When the animation is over the crossbow is unequipped.
I haven't seen any NPC's able to fire the crossbow either. The only instance I've seen is where Isran gives the farmboy (forgot his name) a crossbow and he expects both of you to test it out. I finally got mine working, but farmboy just stands around holding the crossbow by the end in an unarmed fighting stance. I haven't played much farther than that to see if other NPC's are having that problem to keep from ruining the story/making it difficult to use for myself (I sneak a lot).
I'm not using any mods either.
I haven't seen any NPC's able to fire the crossbow either. The only instance I've seen is where Isran gives the farmboy (forgot his name) a crossbow and he expects both of you to test it out. I finally got mine working, but farmboy just stands around holding the crossbow by the end in an unarmed fighting stance. I haven't played much farther than that to see if other NPC's are having that problem to keep from ruining the story/making it difficult to use for myself (I sneak a lot).
I'm not using any mods either.