With regards to Cayde, lore from the first game and the TTK Collectors edition book (with annotations 'by' Cayde), seem to point at him contracting for Clovis Bray. After an incident that left a research/space station damaged, he essentially paid off his debts by going to do a job for Clovis Bray. Possibly giving himself up to science.
" Saturn. No, someplace else. Someplace colder.
This moon has been almost completely converted, a SARCOPHAGUS of ice and iron.
Stone towers run round with glaciers, rooted deep within a heart of snow.
I came here flesh and bone.
Gave everything to the ice.
Started over.
Rebooted. "
until