What if their church or religion says they can?
Their religion can say that a cat is an eagle but doesn't mean the cat will be able to fly. Reality is reality.
Then they follow a group of people who have man made beliefs and don't follow God. It's their choice to chose depravity but....
1 Corinthians 6:9,10 "Do you not know that the wicked will not inherit the kingdom of God? Do not be deceived: Neither the sexually immoral nor idolaters nor adulterers nor male prostitutes nor homosexual offenders nor thieves nor the greedy nor drunkards nor slanderers nor swindlers will inherit the kingdom of God".
Their church can say that they are now trees.
Doesn't make them trees.
This question does not make sense - a man cannot be a wife and a woman cannot be a husband. That is language. Their church or religion can also declare the sun rises in the west and sets in the east - that doesn't make it so...unless they are on Venus.