Interestingly the lounge policy of ‘One World’ members is not uniform has was suggested earlier in this thread with the CX offering being rather more generous than BA.
As a diamond invitation member of the Cathay Pacific Marco Polo Club I am allowed 2 guests in FC lounges even if the guests are not flying with CX. (as are diamond members)
If I nor my guests are traveling CX Cathay offers the use of the BC lounges for up to 2 guests This is very useful for airport meeting and of course for family.
Last year at LHR T5 we no problem entering the BA FC lounge (self,wife and son) using the CX One World elite tier card when traveling on BA and so entry to BA lounges looks rather like the ‘luck of the draw’.
While I fully agree with the majority opinion that vouchers and family memberships are both unworkable and undesirable perhaps BA should consider also allowing 2 guests for their top tier members