YOU SAID:

I thought my cousin married my brother but apparently she married my sister

INTO JAPANESE

私はいとこが私の兄と結婚したと思ったが、明らかに彼女は私の妹と結婚した

BACK INTO ENGLISH

I thought that the cousin got married to my brother, but obviously she married my sister

INTO JAPANESE

私はいとこが私の兄と結婚したと思ったが、明らかに彼女は私の妹と結婚した

BACK INTO ENGLISH

I thought that the cousin got married to my brother, but obviously she married my sister