Note: These criteria must be satisfied by applicants who are members of the family unit of an applicant who satisfies the primary criteria.
887.31—Criteria to be satisfied at time of application
The applicant is a member of the family unit of a person who satisfies the primary criteria in Subdivision 887.21 and made a combined application with that person.
887.32—Criteria to be satisfied at time of decision
The applicant continues to be a member of the family unit of a person who, having satisfied the primary criteria, is the holder of a Subclass 887 visa.
(a) satisfies public interest criteria 4001, 4002, 4003, 4004, 4007, 4010, 4020 and 4021; and
(b) if the applicant had turned 18 at the time of application—satisfies public interest criterion 4019.
The applicant satisfies special return criteria 5001, 5002 and 5010.
If the applicant is less than 18, public interest criteria 4017 and 4018 are satisfied in relation to the applicant.
Ok, so nowhere above it says that the secondary applicant must meet functional English requirement. But yes, I do see that they have that written on their checklist at immi.gov.au. I guess its best if you send an email to firstname.lastname@example.org for further confirmation. This way you have what they want from you in writing as well.