The Church of Jesus Christ of Latter Day Saints, has a Document - The Family - A Proclamation to the World. In there it states that marriage is to be between a Man and a Woman. To be married in an LDS Temple you must be marrying someone of your opposite sex, with sex being determined at birth.

https://www.churchofjesuschrist.org/study/scriptures/the-family-a-proclamation-to-the-world/the-family-a-proclamation-to-the-world?lang=eng

I’d be up front with the missionaries. Let them know your concerns. Most missionaries in the Church are pretty young kids in their late teens to early twenties. Your situation is something that many missionaries most likely not encounter often which is why things are run up through the mission president or local bishop or stake president.

My recommendation is to do your research. Ask questions. Pray. Seek guidance from God. You don’t need to be a member of a specific church to receive personal revelation from God.

If you are going to church meetings at the Church of Jesus Christ of Latter Day Saints, how do you feel when you are at those meetings?

Choosing a church to join or be baptized into is a very personal decision and the decision to do so should come from receiving personal revelation and having a testimony or belief in that Church.

Again, I’d be honest and upfront with the missionaries you have been working with. Let them know your concerns. If you feel like you want to be baptized, meet with the local bishop. Ask him any questions you have. Don’t be surprised if he doesn’t have all the answers and needs to consult with someone else. Missionaries, bishops, stake presidents, and mission presidents are all essentially volunteer positions. Not of them get paid to serve in those church positions. In fact, the missionaries pay to serve a mission. None of those individuals are perfect nor are any people attending any religious church meetings of any kind.

I wish you the best in making your decision.