@twinklecake Like Whimsicat said, it's shortened.
The kanji 兄 means (older) brother. Read as Ani, if you add お it's onii, and then you add the honorifics, all of that in hiragana.
The kanji 義 means whatever, I don't know. It's read as Gi in this case, and when you add it to the kanji above, it means brother-in-law. The whole word itself is read as Gikei, but it isn't used as such when spoken, instead you write it as brother in law, but just say nii-san, or whatever else, omitting the 義.
The kanji 兄 means (older) brother. Read as Ani, if you add お it's onii, and then you add the honorifics, all of that in hiragana.
The kanji 義 means whatever, I don't know. It's read as Gi in this case, and when you add it to the kanji above, it means brother-in-law. The whole word itself is read as Gikei, but it isn't used as such when spoken, instead you write it as brother in law, but just say nii-san, or whatever else, omitting the 義.