Spoilers obviously but if you want to know the important choices, companion recruitment and companion death here is where all the action are.

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Companions you killed off in story like Koth, Aric Jorgan, Kaliyo, Scorpio, Torian, Vette can be reacquired at the companion locator terminal in Odessen alliance base for everyday use. For story purposes they are assumed to be dead and won’t play any role.

I don’t know if you can get Senya/Arcann back this way, will need to double check.
Chapter 1

If you want to recruit Arcann as your companion, you must spare Senya and let her heal Arcann. Arcann will join you in Chapter 6. Otherwise you can kill off Arcann in Chapter 6.
You can kill Senya here and remove her presence from the story.
Chapter 2

You can kill off Saresh and Lorman here in this Chapter.
Acina will join you as a temporary companion in this Chapter.
Chapter 3

You can finally kill Koth here if he left your alliance in KOTFE.
Chapter 5

Koth can rejoin your alliance in Chapter 5 if you allow him.
Chapter 6

Arcann will either join your alliance here and become a permanent companion or you can kill him depending on your choices in Chapter 1.
Chapter 7

If you absorb Dramath into the holocron in this Chapter, he will reappear as a temporary companion in Chapter 9.
Chapter 8

You have to let either Vette or Torian die, there is no happy ending where both lives.
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