The first "Brethren" were about 8 people who left the Radical Pietist Movement, which was made up of folks who had left the Lutheran and State Reformed churches. The Radical Pietists rejected "organized" religion, blaming church authority and structure as the problem. Those who became the "Brethren" believed that the Holy Scriptures showed us that we should be an organized assembly following Jesus Christ.
They rejected infant baptism, as the Scriptures teach that Faith and Repentance comes first. The mode of baptism comes from the earliest recorded baptisms of the Christian faith, three times immersing, or "Dunking" in the name of the Father, and the Son, and the Holy Ghost. This is why they were labeled after coming to North America. Folks tried to figure out who these people were, and the word spread that these were German Dunkers, as most anabaptists and reformed churches practice sprinkling, or pouring baptism, called aspersion. So the German Baptist Brethren didn't give themselves their own name. They referred to one another as "Brethren."
Now I'll try to give clarity where Jordan was inaccurate. Normally a "Cult" needs three different aspects to be called a cult. 1. A separate culture from the surrounding people. 2. A high level of control over its members with strict rules. 3. A dynamic and charismatic leader. If any one of these characteristics is missing, the movement in question is probably not a cult.
1. The Brethren never had centralized leadership by any dynamic or charismatic founder or leader. They don't have a "Pope." And they still don't have any, as each congregation has multiple elders and deacons. And almost all decisions in the church are only approved through voting. And every Baptized member has the same voting power, clergy and laymen alike. The Women vote as well, except at the Annual Meeting.
2. Though most get married young, there is no expectations that you "should" marry at any particular age, and if you want to stay celibate, that is acceptable. Many do get married in their mid twenties and even thirties.
3. A married person whose spouse has left them isn't necessarily lonely as he said. The Brethren are a community, and emotional and relational support is there for the unfortunate situation. By remaining unmarried, they try to be reconciled to the original spouse. They are free to remarry if their spouse dies.
4. The Brethren have no written or unwritten rules about birth control, and many (maybe 50%) would use some form of contraceptives. In fact, it is very common for a lady to wear her wedding dress on her first anniversary. So many of them might not have their first child for 1 or 2 years. If there is an opinion regarding birth control, it is usually some family tree within the church, but it's not a part of any religious dogma.
5. Most Brethren families have an average of 4-8 children, NOT 10-12. And I can name (using fingers and toes) all the families that have more than ten children. Now, any couple may have as many children as they want, but the church has no particular expectation on the number of children.
6. There aren't any singing events that go on for hours and hours. The longest might be two hours, and you may come and go as you wish. And non-members may come if they wish. In fact, there are often the siblings of members at the singings.
7. There isn't any "rule book" for the Brethren. They are non-creedal. Meaning there is no "statement of faith" stated by the church. They have always said that the New Testament Scriptures are their Creed. The "minute book" Jordan referred to is the recorded proceedings of the Annual Meeting where congregations bring questions of faith and practice to the entire brotherhood. And what is decided is taken by voting all the Male members of the church.
8. Any member may leave the church if they no longer desire to stay, and no coercion is used to keep them in. This can be easily seen as the overall retention rate of the Brethren isn't higher than 65%. And those who leave may continue being friends with church members, though the Holy Kiss is no longer shared and the communion bread and wine isn't given to them either. The hardship experienced by some who leave the church is similar to a friend of yours who ditches you for getting married or no longer wants to hang out with you doing the things you always did. But I have seen friendships come back after the initial sadness is over.
9. The Deacons do not read the Hymn before it is sung. Never really have. One of the elders reads the words of the hymn, and a deacon may or may not start the tune, as anyone from the congregation may start one. A deacon usually starts it though.
10. The Brethren use multiple translations of the Holy Bible, but use the King James version on Sunday mornings for continuity. But even in the sermon, alternate translations of the Bible might be cited to give greater understanding of the text. And Greek and Hebrew origins are used for textual understanding.
11. The Brethren may have health insurance (health sharing plans are encouraged) and charity donations are also heavily used. No one is looked down on for having a conventional Health insurance coverage plan.
12. There is no tithe taken by the church. All financial contributions are freewill offerings, and may be any size. Only the Deacons might know what some give, but most donations are autonomous and at the quarterly council the eldest deacon gives a report of the treasury and the expenses from the last quarter.
13. The "Broadfall" trousers worn by the baptized men is not inconsistent with the use of phones or eyeglasses. They are Homemade. They are simply zipper free. With the constant change of clothing styles, Homemade is a way of being consistent.
14. There is no "position of power" in the church. Only degrees of responsibility. The Presiding elder has the most responsibility in the congregation, and every congregation has one presiding elder. But he has no more power of decision than any other member. He can call a council meeting as he sees the need, but that is about it. The elders and deacons are always elected by the congregation.
15. Fiction novels and books are read very much in Brethren homes. Most middle aged German Baptist men now have read all the Hardy Boys Novels when they were young. Some of the most conservative ones that I know read C.S. Lewis and J.R.R. Tolkein, as well as other authors.
16. Higher education is allowed for occupational purposes, such as engineering, or medical. Professional Higher religious education is discouraged, though some still take it. Those who take it are not excommunicated. Most get a high school education.
To wrap up my thoughts quickly, I would like to point out some things that are stereotypical signs of a cult. Special dietary laws, forbidding certain foods, arranged marriages, rules on how you have sexual intercourse, corporal punishment of children, special child-rearing guidlines, coerced membership, travel restrictions, special new spiritual revelation, etc. All these are non-existent in the German Baptist Brethren Church.
I hope you get some inspiration from this info. If you have any questions regarding the Brethren, I have most of the information you would be looking for.