The 80D is will be the best of the lot. The 80D is a mid-range body and it starts to get features normally found only in higher end pro bodies ... like auto-focus micro-adjustment (AFMA) so that if your AF performance isn't nailing focus for a particular lens you can teach the camera to tweak it so that it *does* nail the focus. It also has a bit of weather seal treatment (it is not water proof, but it does have resistant to light spray and dust).
The 77D is actually a T7i in a different body ... and they add an LCD panel on the top and a 2nd control dial. The sensors and processor is identical.
ISO is ... not a "real" thing. You cannot change the sensitivity of the image sensor. What you *can* do is manipulate the data before you write it to the memory card. And that's all ISO really is (on any digital camera).
On a Canon, the camera takes the shot (at the base ISO for the camera). If you've dialed in some increase in ISO then... AFTER the shutter has closed and the shot is over, the camera will apply a bit of analog gain, run the data through analog-to-digital conversion, and then if needed it will apply a little more digital gain. Digital gain basically means it's taking the pixel values and multiplying them by some factor. You literally can do this on your computer instead of in your camera.
You're not really going to shoot at max ISO values anyway (at least you should hope you don't need to). So the real question is, how is the performance at the ISOs that you'll probably be using all the time. The 80D goes to ISO 16,000 (which is far beyond what any photographer should realistically use).