YOU SAID:

youre not going to the party because theyre not going

INTO JAPANESE

彼らは行かないのでパーティーに行かない

BACK INTO ENGLISH

They don't go, so don't go to the party

INTO JAPANESE

彼らは行かないので、パーティーには行きません

BACK INTO ENGLISH

They don't go, so don't go to the party