Be aware that your family may have to split up, depending on the seating configuration on your plane. In many models, there is only one extra oxygen mask per row, meaning that only one parent with a lap baby can be seated in each row. Even if you buy a seat for both babies, many airlines require that car seats be situated only in window seats. Face the facts: parents of twins may have to split up during the flight.
Don't despair; it's actually easier this way. Divide and conquer is often the best approach with twins anyway! Just be adequately prepared for the separation by packing separate supplies for each parent.
If your airline allows you to select seats in advance, choose seats that allow you to be near each other, either across the aisle or in adjacent rows. Bulkhead seats offer more space, but be aware that they don't have storage under the seats and that all your bags will have to be stored in the overhead compartment.
