I am an atheist, so take what I say with a grain of salt. There are many ways to try to reconcile polyamory/homosexuality with religion.
One way is to take a liberal interpretation of the Bible. Basically almost every Christians ignores the Old Testament rules like killing girls for pre-maritial sex, working on Saturday, or being a witch. (Though some try to make the Ten Commandments an exception to this.) So that just leaves the New Testament. Jesus never talks about homosexuality; just Paul does. So you can take what he says about homosexuality in one of the following ways: Paul meant that pagan homosexual rituals are bad; Paul was talking about pedophilia; Paul meant that heterosexual males should not act homosexual; or Paul was just giving an opinion that is not part of the dogma like some of the sexist views on women.
Another route is to go with the philosophy of Christianity instead of the concrete rules. This comes about from Jesus saying that people should not be stoned for the working on the Sabbath as God had commanded. This kind of says that the philosophy should be paid attention to instead of the concrete rules. So a person can go with morals based on th Golden Rule; helping the needy; and being self sacrificing.
Another route is to go with different outlook on religion in which God is more about love than hate. With this idea, homosexuality is a way to express love and God would not be against that. It also pushes the question of why would God make people gay and deny them happiness if he was a good deity.
The weakness of this is that each of these are ultimately the "salad bar" approach. It is picking and choosing religious dogma based on desire for it to be true than on any other criteria. Conservative Christians will typically point this out. A rebuttal to this is that all Christians pick and choose their beliefs in a similar fashion. For example, conservatives may turn away gay people but ignore slothful or gluttonous people even though they are all equally "sinful." Another example is that Jesus said the Old Testament laws would not go away until Heaven and Earth pass away. Yet it is very rare to see a Christian try to live by Old Testament laws.
It is tough being comfortable with who you are when you are brought up with years of people telling you different. One question leads to another and it can cause a crisis of identity or beliefs. I think you can only be supportive and be there to bounce ideas off of. Ultimately, each person will have to find their own way.