Trouble and Eve have been around for about 3-4 seasons. How long ago did you stop watching? lol
Trouble (her name is Teresa Rouble or something like that, so Trouble is just a nickname) = Another Grimm who didn't know wtf a Grimm was. Nick shows her the ropes after they discover her and she ends up coming into her own and part of the team. She ends up getting recruited by a government agency to be an agent that fights group called Black Claw (Wesen Nazis...like literally, they reveal Hitler was part of Black Claw). Black Claw is rip now so dont worry about it ;p She is a lot more murder happy than Nick as a Grimm.
Eve: Julliete turned into a Hexenbiest because of some spell. Then she became ultra powerful and evil. She helps with a trap against Nick's mom, which kills her. Trouble "kills" Julliete. Then Julliete basically gets brainwashed/reconditioned into some La Femme Nikita super agent called Eve and works for the same government agency Trouble ends up working for. She doesn't consider herself Julliete anymore. It was a weird plotline.