How do you define a Christian? How do you define what kind of person is your brother in Christ and what kind of person is not?
1 Corinthians 5:11 But now I have written unto you not to keep company, if any man that is called a brother be a fornicator, or covetous, or an idolater, or a railer, or a drunkard, or an extortioner; with such an one no not to eat.
If someone professes faith in Christ AND is aligning their behavior with the Bible, they are my brother. As the verse indicates, they have to both be called a Christian and behave like one.
Anyone who believes in Christ as his personal Lord and Savior is my brother or sister in Christ.
I agree that their actions must agree with their beliefs (i.e. walk the talk), but that does not comprise at all the basis by which one decides whether they are my brother or sister in Christ.
Romans 14 talks about "Cultivating Good Relationships".
Welcome with open arms fellow believers who don't see things the way you do. And don't jump all over them every time they do or say something you don't agree with—even when it seems that they are strong on opinions but weak in the faith department. Remember, they have their own history to deal with. Treat them gently.
For instance, a person who has been around for a while might well be convinced that he can eat anything on the table, while another, with a different background, might assume he should only be a vegetarian and eat accordingly. But since both are guests at Christ's table, wouldn't it be terribly rude if they fell to criticizing what the other ate or didn't eat? **God, after all, invited them both to the table.** Do you have any business crossing people off the guest list or interfering with God's welcome? If there are corrections to be made or manners to be learned, God can handle that without your help.
Do not interpret this the wrong way, this is not an excuse to say that all denominations and religions are variations of the same thing, they are not. My point is that we interpret the Bible differently, such as what we can eat and not eat, but we still believe in Christ as our personal Lord and Savior.