YOU SAID:

My grandfather married my mother and now he's my step dad and mom's my step grandmother

INTO JAPANESE

私の祖父は私の母と結婚し、今では彼は私の継父であり、母は私の継祖母です

BACK INTO ENGLISH

My grandfather married my mother and now he is my stepfather and my mother is my stepgrandmother

INTO JAPANESE

私の祖父は私の母と結婚し、今では彼は私の継父であり、私の母は私の継祖母です

BACK INTO ENGLISH

my grandfather married my mother and now he is my stepfather and my mother is my stepgrandmother

INTO JAPANESE

私の祖父は私の母と結婚し、今では彼は私の継父であり、私の母は私の継祖母です

BACK INTO ENGLISH

my grandfather married my mother and now he is my stepfather and my mother is my stepgrandmother