DERP, yes go ahead and read/mention anything from my characters' minds you want.

Aeris's brain probably sounds a little different, maybe louder, fuzzier, greener. Not SUPER EXCITING in any way, but just a little clearly weird. She hears the voice of the natural world around her (which in camp means she hears the dirt making a lot of YOUR MOM jokes). Hearing Aeris's mind is probably very serene. She's a sparkling Mary Sue made of white magic and flowers and spring rain, sssso yes. Happy brain full of healing and nature and love. There's a lot more to her than what she's saying out loud at the time, but she's not deceptive. If she's acting friendly and concerned, she's probably thinking friendly and concerned.

Needy forcuttingboxes is a fairly insane cannibal demon. So mostly you can hear HUNGER!!!! but also a fairly cacophonous medly of contradicting desires and personality. Not fun to listen to!

Lady welchersmaycry is a totally normal human, though she's trained herself to be a little quieter psychically, but not in any sort of super-human way, just in a way where she's a well-guarded person. What River can hear is probably just very factual surface thoughts, but there's a lot of calculating going on underneith.