If two homosexuals were married to each other, would sex between them be legitimate?

The reason homosexual acts are wrong is not simply that they take place outside of marriage, but that they are contrary to natural design. For various reasons, both inside and outside of their control, some people have desires that are not in accord with nature. When these desires are acted upon, the result is an unnatural and immoral act. Even if two homosexuals were "married," they would still be having unnatural sex.