Thank you for your excellent response - It covers the subject well.
I have imposed on you I know, but again I thank you for your thought-provoking reply.
A congregation has a responsibility to ensure that truth is taught by its members, and that would include the preacher. "Now I urge you, brethren, note those who cause divisions and offenses, contrary to the doctrine which you learned, and avoid them. For those who are such do not serve our Lord Jesus Christ, but their own belly, and by smooth words and flattering speech deceive the hearts of the simple" (Romans 16:17-18). Just because a preacher teaches something, it doesn't mean that it is the truth.
The ones given primary responsibility in this area are the elders of a congregation. Who are "holding fast the faithful word as he has been taught, that he may be able, by sound doctrine, both to exhort and convict those who contradict. For there are many insubordinate, both idle talkers and deceivers, especially those of the circumcision, whose mouths must be stopped, who subvert whole households, teaching things which they ought not, for the sake of dishonest gain" (Titus 1:9-11). But even without elders, all members of a congregation should be concerned about the accuracy of the things taught.
When there is a conflict between what is taught and what is believed to be the truth, a congregation should follow the example found in Acts 15. Here the church in Jerusalem was notified that some of its members were teaching that Gentiles had to become circumcised upon become a Christian. This matter was debated by the leaders of the church in front of the entire congregation. The congregation, in this case, came to the conclusion based on the evidence found in the miracles seen and what the Scriptures taught, that those teaching the need for circumcision were wrong.
But in your case, it is not a question of false teaching, but a dictating of what topics are to be taught and when. I could see a congregation telling a preacher, "You know, you have been teaching about marriage, divorce, and remarriage for the past two years nearly constantly. We would like you to move on to other topics." This would be encouraging a preacher to do as Paul, "Therefore I testify to you this day that I am innocent of the blood of all men. For I have not shunned to declare to you the whole counsel of God" (Acts 20:26-27). I've seen preachers get stuck in a rut and a nudge to get them back on track is sometimes necessary. Unfortunately, you have the opposite case. You are being told what to teach and when to teach it.
Why not ask for a meeting of the congregation and ask in this public forum why it is felt that the topic selected is not Scriptural ("Oh, it is?"), then why is it not needful for the congregation to learn ("Oh, it is?"), then why are some objecting to truth being taught? What should develop is that everyone will see that it is simply a matter of a few not getting their way and a feeling that they are losing control -- control they never had in the first place.
If in the remote possibility that congregation insists on staying with only a few topics, politely let them know that you are not prepared to rehash old topics at this time. If they would like to find another teacher for the class, just let you know. If they do go so far, then announce to the congregation that you decided to hold a special series of classes in your home on another night and those interested are welcomed to come. This will get you out of being told what to teach and meanwhile you can continue to teach what you see is needful for the congregation.
Paul told Titus, "Speak these things, exhort, and rebuke with all authority. Let no one despise you" (Titus 2:15). Since you are doing what is right and proper for a preacher, don't let others brow-beat you into doing something that is not right. Politely, but firmly, stand independent of those who try to make you into a puppet.