Does the church of Christ believe they're the only ones going to heaven? My brother married someone that goes to a church that's a hard-core church of Christ. He's going nuts. He will hardly look at my family and argues all the time about baptism before salvation. He has given up on the family for not brainwashing us in his beliefs. He acts like a devil, never smiles or has any fun. We use to all have fun swimming in my mothers' pool that we all put work and money into, and now he won't set foot near it! If this is Christianity, I may not want to be part of it. I believe in God, but I'm not going to torture myself to be perfect. Please let me understand this.
The answer to your first question depends on the meaning you are assigning to terms in your question. If you mean, do you have to attend a congregation that has the name "Church of Christ" above its door, then the answer is "no." The Bible uses numerous descriptive names for the church, such as "churches of Christ" (Romans 16:16), "church of God" (I Corinthians 1:2), "body of Christ (Ephesians 4:12), "kingdom of God" (Acts 8:12), and many others. However, if you mean you have to be a part of the church Christ established in order to reach heaven, then the answer is "yes." You can't pick your own way that you want to go to heaven. "Enter by the narrow gate; for wide is the gate and broad is the way that leads to destruction, and there are many who go in by it. Because narrow is the gate and difficult is the way which leads to life, and there are few who find it" (Matthew 7:13-14).
Not having met your brother, I'm assuming that he has learned a lot about the Bible through his association with his wife. He understands things that he didn't understand when he was growing up. It is quite natural that he wants to share this with the people he loves, including you. It appears you never really considered what God has said about things such as salvation. You have heard things all your life, but it doesn't sound as if you have actually gone and checked to see if what you were told actually matches what the Bible says. For example, the Bible says baptism is connected with salvation. "Corresponding to that, baptism now saves you--not the removal of dirt from the flesh, but an appeal to God for a good conscience--through the resurrection of Jesus Christ" (I Peter 3:21). Saul was told when he needed to be saved, "And now why are you waiting? Arise and be baptized, and wash away your sins, calling on the name of the Lord" (Acts 22:16). When people responded to the first gospel sermon, they asked, "Men and brethren, what shall we do?" (Acts 2:37). The answer was, "Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins; and you shall receive the gift of the Holy Spirit" (Acts 2:38).
My guess is that your brother figured out from reading the Bible on his own that he was taught things incorrectly as he was growing up. Instead of blindly rejecting the truth because it wasn't what he thought, he began thinking for himself. You called him "brainwashed," but I have learned that people have a tendency to accuse others of what they themselves do. Who is brainwashed? The one who thinks on his own, checks the facts, and makes his own decisions or the one who accepts what she is told because it is what she wants to hear?
I found the accusation that "he never smiles" amusing because anyone can tell that you are not telling the truth. Few people never smile. I do genealogy and your statement reminded me about something a niece wrote about my great-grandfather, who was an elder in a church in Ottawa, Kansas. She too complained that he and his wife were too strict and too serious for her tastes. More accurate, probably, is that your brother has grown up. He sees the serious danger of your "play" and he no longer enjoys the silly things that you consider to be fun. I remember in high school being asked what we did for fun and I described some of the parties we had and the social gatherings. But he wanted to know if there was booze being served and I told him "of course not!" He truly could not understand how any party could be fun without alcohol. But that was because he could not enjoy other people. He had to be stoned before he could interact.
What happened is that your brother grew up. He is an adult now, but you are whining that he no longer plays childish games with you.
In regards to the pool, I suspect that your brother is concerned about the lack of clothing being worn while you swim. I suspect that he would rather not see his family half-naked. Even though swimming is fun, he made a conscious decision that keeping his thoughts pure was more important than momentary fun. I would suspect that if the rest of you volunteered to wear modest attire for swimming, he and his family would be willing to join you. But likely, he made a polite request, and you laugh at him for being silly and insisted that he must lower his standards to meet yours. When he showed more backbone than that, you decided he didn't know how to have "fun" anymore. He chose to avoid the issue by simply not swimming anymore with the family.
You claim to believe God, but I can see that is not really true. Your wants and desires are much more important to you than learning what God says is good or bad. The sad thing is that you are focused on things that won't last. The things you declare are "fun" are things of this world. And so, because they are available to you right now, you have no interest in eternal life. "By faith Moses, when he became of age, refused to be called the son of Pharaoh's daughter, choosing rather to suffer affliction with the people of God than to enjoy the passing pleasures of sin, esteeming the reproach of Christ greater riches than the treasures in Egypt; for he looked to the reward" (Hebrews 11:24-26).
I hope one day you too will grow up like your brother.