The second is related to the writing of the characters. I don't agree that they "need to be nicer." However, the companions are weird, particularly if you (as most people do) play a custom character rather than an origin. The companions are extremely overwritten in terms of their backstory - not only as companions, but as potential origin stories for the PC. I always look to Dragon Age:: Origins as an example that got things right here, insofar as you actually play your prologue, giving you a backstory, but giving you some agency within that backstory. But in general, there's just...too much...in the background of most of the characters for level 1 adventurers. Occasional banter while adventuring and boning aside, they also don't interact with one another very much. Often there's literally nothing to say to certain companions until you advance their personal quest. This is a problem, because it make the companions not feel like people, but like questlines/stories awkwardly ported into the game.
I also feel like while the backstories are incredibly fleshed out, the actual characters motivations are relatively opaque. Part of this is the weird decision on the part of Larian to make every companion a mystery box - which doesn't open for every companion in every runthrough. Some level of this is fine, but it also means unless you pay close attention to what a character approves and disapproves of, you don't really understand their worldview.
Finally, although the origins are quite...involved...they are also random - at least so far. You can generally go one of two ways with companion backstories. One is to have companions who are relatively shallow - like say in the BG series. Another example is characters who have a deep backstory which is tied into the main plot. Planescape: Torment is a good example here. If you have a deep backstory but it seems to be sort of random within the setting, you end up with...well...Fenris from Dragon Age 2, a character who just seems ported from a different game.
As for your second point - generally agree. I think the problem here, more than anything in the game itself, is with the marketing. if you play this game without knowing anything about it, you might discover a lot of things as the game seems to be intended. The best example is Astarion. The game builds the reveal of his true nature very slowly. first you might get small notes and might see him sneak out at night, then you find the drained boar, and then he tries to bite you and only then you are supposed to figure out he is a vampire. I think that would have worked really well if we didn't know he is a vampire for months and his picture with blood on his lips wasn't on the loading screen. stupid stupid stupid. same thing with wyll and shadowheart. to summarize, I think this is more of a pacing problem than a writing problem. we know so much about these characters from the get-go, it's just too much. If we compare it to Alistair, we don't know anything about him for (depending on how soon you reach redclif) potentially half the game. but when we do learn, there is a lot to learn, but we already got used to him, learned how he is as a character regardless of his backstory. here we have it backwards tons of backstory with very limited character.
I tend to disagree, and I do think there is a problem with the writing. I for one didn't follow the marketing, and, believe it or not, I didn't know Astarion was a Vampire. Or whatever was up with Wyll or Shadowheart. That aside, let's focus for a moment on Astarion. So you find him, and maybe after some sort of misunderstanding you agree that it is better to work together. We both have a bloody tadpole crawling around in our head, and we both agree that we need to remove it, and that our best chance is to work together. Fair enough up to that point.
So what does he do? He sneaks up on you one night and tries to drain your blood. No matter what he says afterwards, he has proven that he is entirely untrustworthy. Given the situation I'm in, I'd kick him from the group. I have enough problems as it is, I don't need a Vampire in my group that I cannot trust (okey, that seems to be redundant).
As for the others, Wyll and Gale are completely overdone. Their backstories do not link up with what they actually can deliver. Shadowheart and Lae'zel are better in that regard, but swing between arrogance and rudeness. I don't expect them to be particularly nice to me, but given the situatuion, and the fact that we apparently agree that we are better off as a group, I expect something more civil.
So I do have a problem with the writing. So far it seems to me that Larian was trying to outdo what they had delivered in DOS and DOS 2, but they overshot the target.