HI
1. Just by entering a church you are not participating in 'babylon the great' - entering a building (Whether a church, mosque, synagogue, temple etc) is not enough to stain you with sin. What is in your heart and mind that is important and matters to God. If you live a good, honest, Godly life, do you think God would punish you just for entering a building belonging to a different faith? If you believe that building belongs to a false religion, that is in your heart and mind, and that is what matters to the Holy one. Babylon the great sits on many waters, in all nations, entering a building is not enough to become part of her.
2. No Christian churches worship Satan. Note that in Revelations 2:13 it states Jehovah knows your works, 'even where Satan's seat is,' and you who hold fast in his name have not denied his faith. So by entering a building alone you are not denying your JW faith, even if this is where Satan's seat is. It is what is in your mind, Jehovah 'knows your works,' which matters.
3. If you could be disfellowshipped for entering a building, what does that say about the fellowship you belong to? It is not important where you feet tread, it is important what your heart and mind believes, it is important what you follow. Listen to the wisdom of the members of your fellowship, but ensure you are following what is in your heart and mind from your own understanding of Jehovah and the Devine, ensure you are not just following the words of man. You should not be afraid of being disfellowshipped by man, humans, people, it is Jehovah who you must follow, not human statements.
4. Oddly enough JW can fit the Revelations statements of Babylon to other Christians. Just as to JW the Christians can fit the statements on Babylon. You make a choice to what you believe, and how you understand the Holy words in Revelations.
5. Remember that Revelation 1 starts with Jesus Christ, 'to show unto his servants things which must shortly come to pass,' and remember that Jesus Christ entered the Temple of the Jews and drove out all who went into the Temple to buy and sell and were doing ungodly things in this Jewish Temple to God (Matthew 21:12). Remember the testimony of Jesus Christ and look to it to consider whether you are following the code of behaviour Jehovah wants you to follow. If you have an ear, let yourself hear what the spirit says to the churches.
6. Then in revelations 2:9 we have the statement that Jehovah knows the blasphemy of those which say they are Jews and are not, but are in the 'synagogue of Satan.' One can reason that this, combined with Matthew 21:12 where Jesus Christ enters the Temple of Jerusalem, (a 'synagogue of Satan'), Jesus Christ did not become part of 'Babylon the Prostitute' (Revelations 17) just by entering a building.
Thus it is my personal understanding that it is fine for JW to enter a religious building, like a church, attend a funeral or a marriage, or religious service, without becoming stained by what one believes to be their 'false worship.' As long as you hold fast in your own belief, Jehovah will know this. If you are afraid to enter another's religious service because you are concerned you may not hold strong your own belief, Jehovah will know this too, and this shows how weak your faith is. Be true and strong in your belief in your route to Jehovah, God the Devine.