Make sure you have good paragon/renegade ratings. It will be better if you have full renegade. Make sure you check the girl that she mudered's room (this includes all journal entries), and speak to her mother about all possible things. Also, make sure you check out the entire bar before going to speak with her. For example, the guy with the Expel 10 tickets. Avoid the questions about family. And don't mention the girl she murdered. At all.
If you spare Morinth and let Samara be killed, Morinth will join you and will be loyal.
She is a part of Samara's loyalty quest. At the end of the quest, Samara and Morinth will start to fight and enter a stalemate. To add Morinth to your party, you have to choose to side with Morinth in the fight. This choice will kill Samara though.
Thane, Garrus, Jacob, Miranda, Tali, Legion, Grunt, Jack, Mordin, Samara/Morinth. Those are the normal ones. If you get the downloadable ones you can also add Zaeed and Kasumi.
Christianity.
Everything
To make choices that will effect you in a good way
The correct phrase is "come into effect." This is the standard phrasing when referring to something becoming effective or operative.
Effect
To make choices that will effect you in a good way
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The squad members are: Miranda Lawson, Jacob Taylor, Grunt, Jack, Garrus Valkarian, Samara or her daughter Morinth, Mordin Solus, Liara T'soni, Tali'Zorah nar Rayya and Thane Krios. DLC adds Zaeed Massani and Kasumi Goto.
Coriolis Effect