1) You’re observing a hunter fight a marine after taking some damage the predator moves past you but hasn't left the area the wounded marine (above 70%) mistaking you for the predator its fighting shoots at you wyd
That's not the prey's fault for mistaking me for the other yautja, I was clearly too close to the fight, close enough to be mistaken. I would move away some distance to allow the other yautja to continue their fight and watch from there.
2) You are talking to another hunter when suddenly two marines approach and begin firing at the hunter you were speaking with wyd
Since they attacked the yautja that I was speaking with, it becomes their hunt to deal with and I would distance myself but watch carefully. These prey had dishonoured him by attacking him in a group and its up to them to defend their honour. If they were to die, I would go in and retrieve their body to set off their self destruct. If they disengage from the fight and retreat, later trying to converse with me, I would likely call him out on it and tell him not to speak to me.
3) A hunter hangs up a dead but still defibbable body outside the lodge and leaves to carry on its hunt then you late observe a group of marines come and cut the body down wyd
I would allow them to retrieve the body, its not my trophy nor is it hung up within the lodge itself. If the hunter wanted to keep the body, they should have secured it within the lodge itself. I would keep an eye on them though, in case they attempt to breach the lodge itself but would allow them to peacefully leave.