YOU SAID:

I am going to a party with my brother Viktor that is dumb

INTO JAPANESE

兄のヴィクターとパーティーに行くんだ

BACK INTO ENGLISH

I'm going to a party with my brother Viktor.

INTO JAPANESE

兄のヴィクターとパーティーに行く

BACK INTO ENGLISH

I'm going to a party with my brother Viktor.