What determines whether heroes trust each other?

It seems to be based on Factions.

Heroes belong to one of three factions: Crew, Prisoners and Natives.

Crew have medium recruitment costs and high leveling cost. They all have the Got Your Back passive skill.

Prisoners have high recruitment costs and medium leveling costs. They all have the Pack of Dogs passive skill. After level 10 their Defense no longer increases when leveling up.

Natives have the lowest recruitment and leveling costs but are weaker at low levels. They have no common skill.

As a memo:

Got Your Back: +10% Defense when near group members they trust.

Heroes that have it:

  • Nurse Deena Ratchet
  • Elise Ness
  • Ken Massoqui
  • Warden Mormish
  • Chef Nanor
  • Sara Numas

Pack of Dogs: (Self) Attack power +6% when their mates are nearby (ie other heroes from the prisoner faction)

Heroes that have it:

  • Golgy Phurtiver
  • Gork "Butcher" Koroser
  • Max O'Kane
  • Opbot DV8
  • Rakya Pulmoni
  • Troe Pekenyo
  • Josh 'Ntello

Which leaves us with the following as Natives:

  • Hikensha
  • Lady Joleri Tulak
  • Mizi Kurtiz
  • Skroig
  • Kreyang
  • Ayairi Whairydd