Regarding Rek'Sai and her Tremor Sense
Okay so, I believe that right now Rek'Sai's tremor sense can be seen by teammates, similarly to Rengar ult and seeing the enemies. Unlike Rengar, Rek gives up a lot for tremor sense, mostly vision. I might just be being nitpicking when I say this just because I like the champ so much, but I feel that teammates should not be able to see her Tremor sense.
First of all teammates gain the ability to see into the fog of war while giving up nothing while Rek'Sai's gives up a lot of vision for it.
Thematically I feel that Rengars ult demonstrates his ability to hunt down and track the enemies, leading his teammates toward them, hence they see the same red glow on enemies. Sort of like a hunting party following a single tracker through the woods. Whereas I see Rek'Sai's tremor sense as a way of reading the environment while under ground rather than purely tracking down enemies.