how can u tell whether it's done by tatsuki_amaduyu or misato_mitsumi or both, im pretty sure it's either of em (/'v')/...

You follow their Illustration like a stalker and you'll figure out the difference soon enough ^^

But on usual, there's noticeable differences b/t the two even though at times they do look similar.

From what I noticed, Amaduyu Tatsuki makes round-shaped eyes and eyelashes, and the mouth is very close to the chin, far from the nose. Mitsumi Misato's mouth is closer to the nose, and the eyes are less round, like an oval-shape. Also, his characters seems to be taller than Amaduyu's. Well, this is what I could notice, but I still get confused sometimes.