Thanks everyone for the useful information, which has now inspired some further questions

1. I am not sure I understand the recommendations to 'sign up my wife and kid' also. If the have different names and are separate people, how can we accrue miles to the same 'basket'?

2. If I make a booking for 3 people (say me, my wife and my cousin). In the end of the booking you normally get to give the frequent flyer number. So, do I get the miles for all three journeys? Where is the line drawn? Are the miles counted for who pays, or each passenger gets their own miles (back to question 1).

3. If I make a booking for a return trip to Peru, which say uses more than one airline (which can be from different FF programmes), do I have to collect the miles separately, or do all go to the air carrier which cover the longest route or what?

Thanks, and sorry for the hassle.