I really hope they actually are armored...
Recurve Steel Crossbow-
Given their range advantage, we need to outrange them. And this should do.
Cross bows are made of the stock and bow, so..
The bow is made up of steel and wood pieces placed together. the center slopes down before springing up a bit at the end. Wood for the center, then steel, then wood and steel at the end.
We use a steel thread for bow, meant to hold up. It's made of lengths of steel string woven into a thread. Attached to the end slopes of the bow.
Stock is steel and wood, used in such a way to prevent the thing from breaking. All in all, this should give us a long range option, while retaining it's easy size to wield.
Last is the Steel Claw. Wrapped up for better grip, to reload the bow, you place it at your feet and use your feet and this Claw to draw the bowstring. Since we have a Pavise, this keeps them safe while drawing, and makes reloading the crossbow a matter of 5 to 10 seconds, depending on our skill at reloading.
Ah, and can't forget the trigger mechanism, but we know how to make that by now. Just use steel here instead, since this is meant to outreach their range.
Anything I forgot? Wrote this up in one sitting,
Recurve bows are smaller, and hold plenty of force. Not as much as a true longbow, but since this is a crossbow, it can hit a higher energy threshold. Save the monster Longbow mechanism for siege-like weapon designs.