Had some issue ending these peoples quest line and getting them to spawn in their final place in Stormveil. This is what helped me and I definitively recommend keeping them all alive as the rewards are rather nice. In addition to a rare happy ending for them all.
Check these out if you need tips to follow their quest lines:
https://eldenring.wiki.fextralife.com...
https://eldenring.wiki.fextralife.com...
https://eldenring.wiki.fextralife.com...