The gnoll, growing bored, says "Well, I guess we need to start by taking out the ballistas. Meveri seems well suited to that, and I think Tenth, Slut, and myself could likewise make our way to a ballista each unseen.
The halflings will probably start fighting back then, so we should probably open the gate at the same time we start attacking the ballistas, to let Yurgret and our goblin allies in.
Slut and Tenth seem like either or both of them should be able to get the gate open, likely by tricking the halflings into opening it themselves.
Sound like a good plan?"
Not waiting for an answer, he says "Good, let's go." And flies back up over the wall, still in bat form, heading for a nearby ballista.