You have to encounter all of the companions more than once for them to join you. For Trudy (human trap) you need like 3-4 encounters. You can invite Urka to join you the 2nd time you meet her and stay at her camp. You also need 2 encounters for the elf.
I know it would break the game but I kinda just want an Urka mode where she just runs around dominating everything. LIke everything turns into a strength check she automatically wins.