Bottom line for the OP: Get your own Sky Miles number. You can still book one reservation for both passengers, and when it's time to enter the two passenger names, you'll also enter each person's Sky Miles number and then you'll earn miles for the flight. One reservation, but both earn miles.

On the flip side, using miles to purchase award tickets is a little different. You cannot book one ticket for 2 people and use miles from two separate Sky Miles accounts. You can either use the miles from ONE account to book an award ticket for 2 or more people, or if you want to use miles from two separate accounts you'll need to book two separate tickets.