Trying to sort out all of the above . . .
Firstly, it's not the income of 'family members (outside of the applicants)' that's relevant. It's the income of 'non-dependants' living in the same house as an applicant.
If the gross weekly income of a resident non-dependant is less than £189, a deduction of £33.40 is made from the housing element of Pension Credit.
Where the gross weekly income is between £189.00 and £245.99, the deduction is £45.85.
For gross weekly income of between £246.00 and £327.99, the deduction is £75.05.
For gross weekly income of between £328.00 and £407.99, the deduction is £85.45.
For gross weekly income of £408.00 or above, the deduction is £93.80.
If a resident non-dependant is not engaged in remunerative work, the deduction is £14.55. (There are some circumstances where no deduction is made. e.g. if the resident non-dependant is a full-time student).
http://www.legislation.gov.uk/uksi/2002/1792/pdfs/uksi_20021792_280215_en.pdf
I would assume that if an applicant states that a non-dependant lives in their house, and that no other information is made available about his/her income, the maximum deduction (£93.80) would be made from the housing element of Pension Credit.