Our understanding was that she would continue to cover the costs of school enrollment and room and board for the children, which she verbally agreed to pay with the rest of the family.

which she verbally agreed to pay with the rest of the family.
which she agreed verbally with the rest of the family to pay.
of which she agreed verbally with the rest of the family to pay.
both of which she verbally agreed to pay with the rest of the family.
both of which she agreed to pay with the rest of the family verbally.

OA here is B - however, doesn't which always refer to the noun it follows so then here which would refer to children?