No matter it's for primary applicant or for dependant, I believe 180-day ruly applies. So I don't think the following statement is true.
"if the principal is eligible for adjustment of status under section 245(k), the spouse and minor, unmarried children may adjust status under section 245(k) even if they have been out-of- status for over 180 days.
"
If you're sure about this statement, can you share from where you got this info?