Ragzlin, Gut, Minthara etc: These are not reliable evidence sources for us being 'safe' enough to take our time; our tadpoles are clearly not the same a theirs, we know we have them, they don't - they all believe that theirs is a literal god talking to them. Their tadpoles leave their brains when they die, ours do not - any reason you give for this is
You Making An Assumption; it might be the case, and it might not be - you don't know.. There's something different between theirs and ours - would you wager the entirety of your life and your immortal continuance of being thereafter (which in this universe you know that you have, incidentally, unlike ours) on simply "Assuming" that ours isn't going to destroy us or do something else irreversible to us, just because it seems like theirs haven't?
Meeting the true souls does *Nothing* to allay our own concerns, because they are not the same as us. We also don't know where they got their tadpoles, or how, or why - they certainly weren't on the ship with us, after all. It tells us literally nothing about ourselves, and our situation, only theirs.
There is nothing here to tell us, with ANY kind of reliable certainty, that we are not in life-threatening danger.
It should eat your brain > it dont.
If that isnt good thing, i cant really imagine what is.

Yes you can, don't lie for the sake of your stance, it only undermines it. I'm sure you're not that lacking in imagination. As wormerine suggested, and it's more or less a very well fitting analogy:
You stepped on a land mine. It should explode, it didn't. This is
NOT a good situation, and not good news. It is most definitely not something that you should relax about and feel content to ignore and assume you're in no immediate danger - and carry around in your backpack to show to friends - just because it didn't explode already. It should have exploded already, yes - and the parallell here is that it SHOULD have turned us while we were passed out on the beach, and 'we' should not have woken up at all (recall that it we were captured inthe afternoon, spent time onthe ship, had the ship crash duringhte night, but woke up othe beach in the morning - long enough that it should have destroyed our personality already.)
That we are still here is
NOT 'factual proof' that it is not working - it proves only that it's not behaving as our lore books say it should. It is active and doing things though, and we don't know what, or why - the mental connection episodes, are one example, even without actively using the tadpole powers; even without them, too, it's clearly there, giving us that sensation that we cold do something, and we repeatedly are told about how terrible our characters are looking, and that we can occasionally feel it moving in our skull.
Where I disagree with Wormerine is on Halsin: Halsin may be a credible source to tell us that ours is not behaving in the traditional way, but he is not a sufficient information source, as it stands currently, to reassure and take the time pressure off us, in relation to our specific situation - only someone with direct personal knowledge of exactly what has been done to us, and our/or tadpoles - our specific situation - can provide that. Halsin has studied these altered tadpoles, but again, ours are not the same as the other absolutist ones he's encountered. Even then, his only information is that "it's not transforming you when it should - it may not, but it may, and I can't tell you when or why it might, just that it might... but it seems like it probably won't" That alone is not sufficient information to remove it from doing everything we can about it as our no-distractions top priority. If his information was that "You're aware of yours, and the others aren't, but the basic effects seem to be identical otherwise, and I can say that these ones don't transform their hosts on their own - they need some kind of trigger, though I don't yet know what." That would help the situation, though as suggested, removing our knowledge of the tadpole, in universe, would be another possibility.
If you need to presume that the character is ignorant, stupid or reckless (that all of them are, in fact - party leader problem) in order for your game to make in-universe sense, then your game design has failed.