So, you can't just shift alignments on people because my action may SEEM like it is Evil in BG3, but it may actually just be smart. I'm SAYING I'm joining Minthara when I'm really pretending to join her to lure her into a more advantageous position for myself. Instead of 4 party members fighting Minthara in her home court, I'm luring her to a well-defendable gate with allies like Zevlor to help me wipe out her forces. So how is Larian going to judge my action of "Yes, Minthara, I'm going to help you"? Are they going to call that evil?
Well, lying is evil, no?

On top of that you endanger grove and tieflings out of concern for you own safety. Minsc and Boo wouldn't stand for that!
That is unfortunately common problem whenever RPG tries to "judge" players actions. As it is I am everyonce in a while irritated that companions take at face value stuff I say as a PC.
Not necessarily evil. No. This is a common misconception among those who translate scripture. Bearing false witness is evil because you are lying and therefore causing an individual to be convicted for a crime they did not commit. Lying is also not good in most circumstances. But again, lying might be the best option when people's lives are on the line. Again what is right outweighs the rule or law for those who are good.
Again I use the example of The midwives and pharaoh. Those midwives lied through their teeth to save the Hebrew boys from being butchered. God bless them with families of their own and made them prosperous for lying to pharaoh. They did what was good and right in that they saved lives which was way more important than committing an act of lying.
So lying is not necessarily always evil. You see? Alignment is not so black and white.
The same concept could be applied to the situation with the Grove. Which is best? Is it best for me and my companions to die trying to fight these goblins and their leaders in the heart of their den just the four of us? What will happen if we die? Will they not then eventually raid the Grove and kill everyone in it? However, if I lure said leader and a bunch of her goblins too The Grove and help them defend it, now I have more defenders and a better defendable position and we might all survive. This is intelligent and wise tactics, and therefore might be considered actually more good.