Sometimes you hit the limits and there isn't much more you can do.
1) At 1/400sec you're fast enough to hand hold and get a steady shot, plus you've got some speed to account for motion of the subject. Whilst they are at a fairly sedate moment, there can still be fair bit of motion going on. Ears moving, whiskers, fur, legs twitching and mouths chewing. All of which require a faster shutter speed even if your camera is set on a tripod and thus totally stable (thus letting you avoid handshake).
In fact for general wildlife I'd consider 1/400sec to be a risky slower speed and would be happier with 1/640sec at least. However in darker conditions I might risk going slower and crossing my fingers that a quick burst of shots would capture one moment of total stillness of the subjects. I'd typically burst in small groups of 3 shots. Controlled bursts are nothing to be shameful about, sometimes using that digital memory card and large storage space can get you those split seconds that are super hard to predict or even see.
2) Your aperture is wide open for that lens, not ideal in terms of sharpness (you'd want to be stopped down at least one stop from wide open on most lower end zooms when at the long end); but, again, its dark and you're setting your settings for a decent exposure and light capture. Again its a dark situation and you've done what is practical and sensible for that situation in weighting overall exposure over overall sharpness.
3) ISO 12800 is high and that is going to harm the image quality. But again you're at the limits. You might have got an extra stop or two if you'd slowed the shutter speed, but then you'd introduce more potential handshake and subject motion as possible issues.
In the end you've honestly done well and what you've hit is simply the limits of your equipment in a challenging lighting and subject situation. This is fantastic experience for you as its teaching you the limits of your gear. It's getting you to work at the hard end of things and to make those choices on what is important to you in the moment. I find it can also help teach you better editing methods since you are now forced to work on your noise reduction method and sharpening somewhat; whilst good light and easy subjects can oftne let you be really casual about such things.
First bit of advice I was given that helped me the most when I posted a photo "alike" this.
First thing, get closer or a longer lens.
Ahh but you have to remember the inverse wildlife rule. No matter how long a lens you get the wildlife always moves a proportionally further distance away from you to make you want an even longer lens