so you are their...
Step brother
His father...
Her mother...
Half brother
Engagement
Parents
Half sister
Her sister...
Siblings
His brother...
Marriage
So they are your...
Step sister
Relationship
Grand parents

You

Mother

Mom

Mommy

Ma'

Sister

Father

Dad

Daddy

Pa'

Brother

Sister in law

Brother in law

Boyfriend

Girlfriend

Fiance

Fiancée

Husband

Wife

Ex...

Daughter

Son

Aunt

Uncle

Aunt in law

Uncle in law

Grand father

Grand mother

Great grands...

Son in law

Daughter in law

Nephew

Niece

Grand son

Grand daughter

Great grands...

Cousin

Ex...

Cousin

New couple / New Pair

Previous descendants

Step-son
Step-sister

New descendants

Son

Daughter

Step-father
Step-mother