Grove should be in siege mode, with barrels diged in the ground before gates ...
If you dot have that, try to talk with Minthara again ... if she is gone, im affraid you have to reload since that sounds like a bug.
There are two possible approaches:
1) Blow the horn Wyll was using in first battle, that is how you give Minthara signal that you are prepared for attack.
2) Kill everyone in the gate, and open it ... then long rest, Minthara will wipe out the rest in the middle of the night, while you sleep.
PS.: Feel free to repeat this post for him anyone, since he claim that he have me in Ignore list.
