To be clear, Adamar's presence can be described as pure dread. Think of a time when you were truly scared, knots in your stomach, a chill down your spine, etc. His 'aura' is so dense with malice, that it can feel as though a physical force is being exerted on them, inducing anxiety and to those with a weaker constitution, breathing might become more difficult. It's similar to when someone has a feeling that something bad is going to happen, each denizen of the realm would feel like he was looming over their shoulders, to the more susceptible to intimidation it may feel like a gloved fist around their throats. To animals, especially familiar's, these feelings and exertions of presence would be magnified, as animals can sense danger more keenly than most. They won't know -what- it is, but they will know it is unnatural.
Morris should be the only individual truly unaffected by Adamar's ostentatious display of his aura, as they've associated many times and he is virtually immune to it. I'm aware that everyone reacts to fear, paranoia, anxiety differently so I don't expect everyone's reaction to be the same.
For those unaware, he is currently in the Aether, attempting to pierce the magical barrier keeping unwanted intruders out of Nautchwald, similar to standing on the opposite side of a mirror. He can peer into the realm, but it won't be until Gwen and Ana finish their part that he succeeds. So, in a manner of speaking he has been stalking and shadowing the witches for awhile now and is readying himself to acquire Moselle. It's worth noting that the familiars in Moselle's room will more than likely be the first to encounter him.