Foreign names are almost never written using kanji - they are written inkatakana. In katakana, the name Aaron would be アーãƒãƒ³ (aaron).
A possibility in kanji would be安論 (aron), but I strongly advise you not to use it as your name.
We write it as 鯉[koi] in kanji in Japanese.
There is no Kanji for "madsam."
you can't
龍 or 竜
'Ojiichan' written with kanji isお祖父ちゃん.
you don't its written in katagana
jishin 地震
酒 is the Kanji for sake.
尊厳 Songen
you don't its written in katagana
櫻.
you don't its written in kanji 日本語 When you write sentences in Japanese you will use a mixture of Kanji, Hiragana and Katakana.