1- In the movie, she mixes her personality with her MOTHER'S - this is grammatically good but does not make sense - how can you mix a personality with another's? 2- Even though he's married he SUSTAINS several parallel relationships. - this is fine, although MAINTAINS is more common 3- in the Cuban religion called “Santeria”, they say that there are spirits which accompany humans. These errant souls fulfill their worldly desires by means of influencing the people whom they accompany.

1) I think this is okay. 2) I'd use the word "conducts" instead of "sustains." I'd also probably say "is conducting" rather than "conducts." 3) This needs some work. I'd suggest: In the Cuban religion called “Santeria”, it is believed that there are spirits which accompany humans. In this way, these errant souls fulfill their worldly desires by influencing the people that they accompany.