ok. that half-ish answers my question. are there characters who totally vaporize people just like aizen?

That total-ish answers your question as your original question is if humans can be killed with simple high reiatsu. Now, can other beings desintigrate humans? They should be able to, the effects of reiatsu is proportionate to the extent of it, so the few chacters comparable to post-Chrysalis Aizen should be able to do similar effects (or even higher effects if they are notably stronger). Of course, this is never shown in-series, as theres no reason for normal humans to be involved in Thousand-Year Blood War arc for them to be desintigrated by the monstruos reiatsu presences there.

Ok chill. I just wanted to know if it was possible for any other beings besides for aizen.

There have been no other beings besides Aizen that have had the chance to show that ability so a clear cut answer isn't possible, although from looking at the various situations in bleach you can naturally infer that hollows can do this to humans when they become strong enough. When Orihime's brother touched her as a weak hollow, there was a burn mark and it's not unreasonable to assume that stronger hollows could do more. Then there's starkk and lilynette, they unwillingly killed other hollows with their mere presence by accident so the odds a human could survive that are very small, meaning the human would to some extent die (not sure if they'd disintegrate like with Aizen though). Though keep in mind that since there's never been canon evidence proof one way or the other, the question is technically impossible to answer

say, was the stark-thing before or after his separation?

Absence of evidence is not evidence of abscence. Reiatsu mechanics have been concretely explained, for Aizen him desintigrating things in his surrounding was a byproduct caused by the intensity/amount of power he had reached. Thus since reiatsu is a scale in Bleach, anyone with a reiatsu of similar or higher potency would be able to produce similar results. Factuality isnt determined solely by visual evidence, but by a compendium of general evidence producing a conclusion, in this case the series itself providing sufficient evidence for a factual conclusion to be reached.

yes, I get that. by the stark-thing, I meant 'was he killing hollows before or after he separated his body in two?'

True, but the whole premise of critical reasoning is taking certainty you can observe and building a theory from that. In this case I think you are wrong because besides hollows, elemental aspected shinigami, and transcendent powered people, shinigami have never shown direct destructive capacity with reiatsu alone. They have messed with the mind, bolstered physical capabilities and created elaborate abilities but never caused raw destruction with reiatsu. Aizen was a bad example because he wasn't a shinigami anymore and seeing how there are many things shinigami can do that hollows cannot it is not unreasonable to assume that what reiatsu can do is highly determined by their species, basically the amount of reiatsu is less important than the quality/type that they have. I am open to being wrong so if you can show me a statement from Kubo or canon evidence that you are right I will gladly except your opinion (though I may discount it if you have examples with the irregulars Kenpachi or Ichigo, since they break the rules in many ways).

Also, to answer the last post, they killed hollows after they split and very likely before too (though I am a bit of a stickler in saying that lilynette and starrk are technically one being so her reiatsu likely contributed as well...I have no real evidence to back it up but my thought has always been that she just does not have the control to properly use her power for her own benefit so she seems much weaker than she actually is, I mean it seems unrealistic to me that starrk would get such a power boost in ressureccion if she wasn't strong too)

I think it should be quite easy for a capitain-level character to kill a human with their reiatsu. Stark created Lilynette because he was feeling alone, since only his presence was enought to kill other hollows...

Like I mentioned earlier, there's not a single bit of canon evidence that a shinigami can kill with reiatsu alone, though there isn't evidence to prove me right either my speculation seems more correct since hollows naturally hurt things with their touch and even a shinigami like kenpachi, who was known for epically poor reiatsu control and gargantuan reserves of power, wasn't killing weaker shinigami with his mere presence like starrk and lilynette were with hollows. I also have to contest the"fact" that starrk created lilynette. Starrk admits they don't know who came first, just because lilynette is weaker doesn't mean she may not even have been the original (possibly made weak the way a shinigami was vastly weakened by losing their zanpakuto spirit in the muramasa arc, she could have done something like externalized her inner hollow and lost most of her power as a result), and in the first meeting of starrk and lilynette she seems to me to be somewhat less confused by the situation almost as if starrk was the newborn, not her. I'm not even saying she was the original, just that to my knowledge Kubo never revealed anything about their past as a hollow so it's a huge leap to speculate that starrk was the "real" one, especially when an equally good case can be made for her or even neither. Sorry for the tangent, I just don't like people assuming on this issue