Another possibility, that avoids battling several bosses without long rest, is as follows :
1. Liberate Halsin from the worgpens : Make sure no goblin escapes to raise the alarm ! When Halsin is free, tell him to stay put til you return. Don't let him acompany you.
2. Go to Minthara and tell her you know the location of the grove.
3. Prepare for the grove attack (position oil barrels) and take long rest.
4. When the goblins attack, betray Minthara and fight with Tieflings. Dispatch all goblins but knock minthara out. You can loot her, but leave her lying where she fell.
5. Now you can go to your camp to celebrate with the tieflings.
6; Return to the goblin camp, which is now hostile and defeat the goblins and their leaders, in whatever order you want. Long rests can now be made.