That advice is the most important of all -- if you book as separate purchases, then there are two individual tickets, and his benefits will not accrue to you. You need to make one purchase for the both of you together, on the same itinerary, so there is one PNR (Passenger Name Record), and therefore one Record Locator (sometimes called a confirmation number). Doing so, the two tickets will appear as linked together and 1K benefits will be shared with all travellers on the PNR (up to 8, if memory serves). There is no other way to link tickets together, and it can only be done at time of purchase.