Personally I think a lot of why shes dismissing what he has said is because it hasnt happened before to her knowledge, she doesnt want him telling the wrong person, but if she doesnt try to believe him, thats exactly what will happen, hes already stuffed up and let the wrong person hear something, twice... Laurie and Astrid, luckily that has been dealt with already.
I think she wants to believe him, but if a friend walked up to you and told you he could see the past etc, what would you think, the first thought would probably be "Your Crazy", but deep inside you would want them to stop, so that you could go back to believing in them.
Sharon believes the MC about the Invisibility and Claws, but the Whispers were something she couldnt see, like his visions, and they will need to work through that before something goes bad.
BTW the visions dont appear to be one of his Disciplines at all, remember there was also that Nos that was having the same sort of visions, I think thats more due to the "Blood Queen" - Woman in blood whatever we wanna nickname her, from what we have seen she is ancient, probably was ancient even when the MC's Sire was a Childe, I suspect she is Antideluvian which would explain the visions, maybe that Nos is of a similar generation to the MC, I cant remember the exact comment but I think Merrik said the guy was powerful before he started having visions, and only those of a powerful Generation are getting the visions, it would explain a lot, she opened the door, and the MC is looking through - so to speak, essentially a free forth Discipline.
But yeah, Sharon needs to listen, and he needs to explain what hes seen, to those he trusts, Sharon and Laurie, Andrew to a lesser degree but thats because he does what Sharon says, MC trusts Merrik but some of what he has seen and done has to be kept from him, so yeah...
Carmen, is a problem, there are two different choices to make, Live and Die, and if Live Thrall or Vamp, they all know if she becomes a Vamp there will be trouble, so that kinda removes that option in the shortterm, so its really Die or Thrall, if Thrall who's Sharon, Merrik, or the MC, If she was a blood bag to the MC then Merrik is the main option, as then he doesnt have to worry about borrowing Laurie which most MC's would be against due to their lifelong friendship, Sharon even said at one point that the MC could use her as whatever he wanted, she was going to give her to him.
If the MC was nice to her, then the chances are he'd want Carmen to be either his or Sharons, but they might be willing to let Merrik have a bite if needed since they arent long time friends.
Back to the talking between the group I think the MC and Sharon need to talk before he takes a walk in the sun due to her treatment, when your dismissed like she had done theres no idea what you might do, especially when you might have a vision and walk outside during it...
Once he is able to tell her some of t he things hes seen that she knows are true, she might open up, sure his clan is different but so far nothing about his clan has been of a disadvantage, Sharon will see that and be able to convince him to not talk about the bits he needs to keep quiet about, heck his Sire could even turn up and explain it to her, but that would be a bit overkill.
Also I think she knows how potent his blood is, when she got hurt she was close to final-death, a small drink and she was fully healed, needed a little blood to be full but still, that happens only when the blood is especially potent, and she would know it, she is fond of him though so she doesnt want anyone to hear about it, fearing he might get bled for that same blood.
In relation to the whole dick twitch incidents, Laurie I think was the first to cause it, then Sharon, both a few times, then Carmen eventually, It had happened in Episode 1 so yeah, its not all because of Carmen like a few people have mentioned.