Now that I've had the time to look at your agent bios, both together and separately, I'll spend some time with both general thoughts and each of them. I'll preface this by saying that I have constructive intents here and I don't mean to be demeaning. (Of course, my own experience with such a disclaimer implies that some things about your bios don't sit well with me, but hey, that's what concrit's for. ^^;)
First off, Scapegrace is correct in that first-time agents don't have to be human. Looking at a lot of Permission prompts and starting missions my fellow Boarders have written, I believe the reason so many people go with human agents as a basic "starting kit" is that, as TV Tropes puts it, Most Writers are Human. This means people are much easier to write for us than non-humans are, because we relate to other people much easier than we would a bird made of knives, a nine-foot-tall insect, or for that matter, a fire-breathing dragon. We tend to see monsters as, well, things, and not characters, which is why so many horror movies nowadays don't leave a lasting impression. I think the scare could be greater if you can relate to the creature in some way. On a broader scale, unless you start with a species that's already subject to some degree of anthropomorphism, such as a Pokemon, a non-human agent is a greater challenge than a human one, but has the benefit in that you don't have to stick to tradition. It's just a matter of personal taste. I personally find that trying to write a World One agent who stumbled upon the PPC via a plot hole would be boring compared to, say, writing Falchion or Cupid, for example. (Also worth noting is that Darkotas sent in two non-human agents for Permission as well, a Gungan and a Warcraft ogre I believe.) It's harder to build a strong base for either of them than for a human, especially a World One agent with a simple tried-and-true formula, but I can say with confidence that it's not impossible by any stretch of the imagination.
With that being said, I had a look at each of your agents, and I feel that while they could use a little work - okay, a LOT of work - you seem to be off to a good start. I'm not familiar with XCOM, but I had a look at the Thin Men, and the first thing that came to mind was the Uncanny Valley. I'm reminded of the agents from The Matrix movies, but with disturbing proportions, acid breath, and so on. The biggest thing that threw me off with his bio, though, was the lack of a History section. Without it, I couldn't really picture how he ended up in the PPC in the first place, which is really important if you want to build up his backstory. Suggestions include either going with the old plot hole trick like with Falchion (albeit with a good explanation as to why the plot hole was there in the first place; just having it show up for no reason would sound like an ass-pull to the reader), being found by an agent group in a badfic as with Cupid or Backslash, or else escaping from a badfic like Lapis. You didn't indicate whether any of these was the case, which really bothered me when I first read the bio, because it made him look as though he only existed to support Carnage (whom I'll get to in a bit). Every agent has a story to tell, and Sesrik should too if you want him to pass as a solid character. Scape made a good point about the Thin Men being essentially living tools without emotion or honor, so exploring how that would mesh with the PPC and its mix of democracy and comedy would be an interesting path to take. Hey, if Chakkik can do it, perhaps Sesrik can too.
As for Carnage... I honestly have more problems with him personally, even though I get what you're trying to do and I can understand why. An agent that's essentially a shrunken-down kaiju would pose some interesting implications, especially regarding how he now lives among the people he once towered over and within the buildings he used to destroy. It doesn't help that I once thought of an Indominus rex replacement as an agent, but I digress. However, when I looked at his bio, I noticed that it was too long. By itself, it's not too bad in terms of verbosity - I myself went into quite a bit of detail with both of my starting agents - but what was really jarring for me was that Carnage's bio was too long relative to Sesrik's. This is the other reason for my sentiment that the latter came off as only being there to support the former. A massive part of the reason for this is that while his abilities are par for the course as far as kaiju are concerned (many of the ones I've created have just as many cool tricks), a human sized kaijin of sorts is a wholly different animal, quite literally so. Carnage could probably wipe half of HQ off the map if he lost his temper, and the bloodlust he has as a "weakness" does not help, especially because if he's going to be an assassin, he'd have to witness the deaths of every Sue he'll come across. (I had the same complaint about the bloodlust lobbied against me when I first introduced Rayner; I've since been sorting it out, but I must say that it just doesn't mesh well with how agents work.) Everything else is reasonable, though I would again agree with Scape's suggestion to make Carnage a Noble Demon of sorts. Kaiju were originally created by war and violence, so it would make sense to have Carnage be born from, well, carnage, and have to live with the consequences. In his case, since he's burned everything, he has nothing left to do, so it's only fair that he starts moving down from the top, taking a good long look at the smaller beings he once lorded over and starting to empathize with them. (As for the shrinking thing, don't worry about it too much - my second DIC mission involved the use of a Shrink Ray to deal with a giant Sonic replacement.)
With all that being said, I'd still give him far fewer powers than he has in this version of the bio. If the technology the PPC has can shrink him, getting rid of his more dangerous powers wouldn't be too much of a stretch. The only powers I'd give him would be his thick, possibly fireproof scales, to contrast with Sesrik's vulnerability (and even then make him vulnerable to certain things like cold), and his fire breath, because, well, he's a dragon. Among his weaknesses, I think the bloodlust has to go, unless you can write it sensibly into the PPC like I did with Rayner and that I highly doubt because, well, my poor pony boy has to take meds to suppress his condition. I will reiterate that a bloodthirsty predator does not an agent make.
As far as final thoughts go, my major piece of advice would be to think carefully about how your characters would work within the setting you're trying to put them in, as opposed to looking at them within a vacuum. This is a pretty common trap for Sues/Stus in general, and believe me, I myself was guilty of it plenty of times back in the day, as if that angry T. rex!Violet I had slain on my very first mission wasn't enough of an indicator. The PPC is not, however, a free-for-all, but a coherent and cohesive universe where everyone has their place, use, and limits. It's important to know in particular what your characters' limits are, and whether they fit the standards of the PPC and its community. I like where you're headed with your characters, but they need to have their capabilities and mentalities not only defined more clearly but also scaled down very much in order to gel with their peers. As it is, I'm not confident in either of these aspects for either of these agents, and until I see a lot more streamlining and tightening for them both, my hopes that they'll get a pass when you request Permission are uncomfortably slim.
Now, then, I wonder if I can get your e-mail? I'd be happy to discuss your agents further and serve as both a sounding board and a beta reader if you need one in the future. :)
-SS