This guide details how to recruit every crew member in Citizen Sleeper 2. Remember, while recruitment is usually straightforward (accepting their offer), success in certain Contracts or events might influence your ability to recruit or retain crew members. Bad rolls can also lead to crew losses. Feel free to comment if you find alternative recruitment methods!
Crew Member Recruitment Guide:
Serafin and Bliss: These two join automatically and are always part of your crew. Serafin is generally unavailable for Contracts. No achievements are tied to their recruitment.

Juni: Initially a temporary crew member on Hexport. Recruit her permanently by visiting Helion Gate after completing the "Idle Minds" clock at Solheim Records. Complete the subsequent Contract and agree to let her rejoin your ship.
Recruiting Juni unlocks the "Data Archaeologist" achievement.

Yu-Jin: Found on Far Spindle after completing the "Getting Wracked" clock at Gaia's Gyre (requires ordering a Wrack four times, costing 16 Cryo). Complete his Contract to permanently recruit him.
Recruiting Yu-Jin unlocks the "The Freelancer" achievement.

Luis: During the Aphelion Beacon Contract, choose to leave Yu-Jin behind to recruit Luis.
Recruiting Luis unlocks the "Signalchaser" achievement.

Kadet: Encountered on Far Spindle after completing the "Spindle Core" clock at the Spindle Core location. This unlocks a new drive and Stripline Express. Complete the tasks at Stripline Express, triggering a cutscene. Then, travel to the Scatteryards to recruit Kadet.
Recruiting Kadet unlocks the "The Spindlejack" achievement.

Femi & Nia: You can recruit only one of them. You'll meet Nia on Hexport and Femi on both Hexport and Floatsam. A Contract involving Nia's safety will lead to a choice between them.
Recruiting Femi unlocks the "Big Brother" achievement. Recruiting Nia unlocks the "Little Sister" achievement.

Flint: After your first visit to Olivera, a Contract will lead you to investigate Flint's disappearance. A subsequent Contract requires setting a trap for an enemy; follow Xander to rescue Flint and recruit him.
Recruiting Flint unlocks the "Fugitive" achievement.

This completes the guide on recruiting every crew member in Citizen Sleeper 2.