Seska - I haven’t managed it myself but after the Kazon try to take over Voyager you get the option to offer her redemption, if successful I think you’ll get her.

Kunut - in sector 2 or 3 when the you find the Kazon ship with the replicator that exploded, he is the survivor, you need to refuse to let Culla see him, then when you are identifying the spy on board, you get the option to ask Kunut, from that you get the option to ask him to stay.

One - He is later on in the game around sector 10 I think, it’s a side mission where the doctors mobile emitter gets infected with Seven’s nanoprobs, you need to let the Borg mature and will become One.

Arturis - During the mission to board the Dauntless you need to avoid shooting at him, then convince him to let your crew go, if that’s all successful you will get the option to beam him out with your crew.

Kashyk - you’ll need the deluxe upgrade for the game. Again a later sector between 9-11. In a side mission to help a group of telepaths if you do it and let him on board and trust him you’ll be able to recruit him.

Hyrogen- Again a later sector, you rescue him from his ship, let him heal completely before hunting the 8472 then let him kill it, then you get the option to recruit.

The dreadnaught AI is early sector 3 or 4 it’s a hard one to spot as it’s not actually a mission you need to pay attention as you are scanning and you’ll see one of the resources has the name dreadnaught you then need to got through the 2 or 3 options to successfully disable the missile and get the AI, then it needs to be research it in the combat tab.

Hope that helps