It can be done.
Tell you what, have Fay roll attacks for the two ballistas, one of them with disadvantage (The one for which Fay isn't there to help with targeting.).
Unless they can garner some source of advantage to counter it, all archers other than Lia firing at the NW group will be doing so at disadvantage thanks to the range.
Edited: daishain on 1st Apr, 2017 - 4:54pm
Got it and I don't mean to look a gift horse in the mouth… just checking. I have an hour to wait before I can post again or someone else has to post over in the main thread before I can.
Edited: Abnninja on 1st Apr, 2017 - 5:23pm