YOU SAID:
My mom is their mom who is their step mom
INTO JAPANESE
私のお母さんは彼らの継母である彼らのお母さんです
BACK INTO ENGLISH
my mom is their mom their stepmother
INTO JAPANESE
私のお母さんは彼らのお母さんです
BACK INTO ENGLISH
my mom is their mom
INTO JAPANESE
私のお母さんは彼らのお母さんです
BACK INTO ENGLISH
my mom is their mom
You've done this before, haven't you.