There must be something simple I’m missing but I can’t get my siege to attack the target i’ve given them, they just head towards that location. How do I unpack them and get them to fire? Thanks
Right click or control A + click on the target ( springyald on mangonel for example)
But to me it sound that you have a problem with line of sight.
Siege needs to have a clear straight line to the target.
So uphill you can’t shoot with a springyald. A mangonel or trebuchet shooting uphill will work.
You can use this in your advantage in battles. Make sure you attack downhill with siege. 
Thanks, didn’t realise that they needed line of sight.