You need to question whether you really need to have the conversation in those terms. A conversation about religion/theology is not like a conversation about physics or math. If you insist on applying scientific rigor to matters of faith, you are and will remain fully confused.
I bet if you observe your own mind for long enough, you'll find some part of your life which requires you to have faith too. Use that to understand your friends and family better. The next time you find yourself in a conversation with them about religion, ask them about their faith (not their religion). You will gain a deeper and more nuanced understanding of how they navigate the world.
If you can have that conversation, go ahead and ask them about their religious beliefs, withholding judgement unless/until they say something morally objectionable. You can think of their religion like any other mythology, and you get to play sociologist for a while. There's a fascinating variety of responses people give to even fundamental questions - e.g. "what is god?".
This open approach is not only much easier for everyone, it's also more useful in the long term. My neighbor has an interesting mashup of beliefs that includes a decent chunk of Christianity. She sometimes has bad anxiety, and unfortunately she can't afford treatment for it. I've helped her out of panic attacks using two methods: 1 - I've given her a clonazepam tablet and 2 - I've quoted scripture to her (e.g. "behold the lilies of the field"). Both methods work, and the latter tends to work faster.
It's different if the person is using their religion as a cover for engaging in or supporting something morally evil. That's a trickier conversation and often one not really worth having, depending on your relationship and how comfortable/willing you are to attempt to correct them.