Careful in my experience holding 2 reservations on one name on the same flight can be dangerous....if the airline notices such a double booking they can cancel BOTH.
Here is what happend to me:
I had asked one TA for pricing on a LH flight (and the TA actually made a reservation which I did not know). As I got a better price from a different TA for the same flight I went with that offer and told the other TA. That company forgot to cancel their booking so there were 2 bookings on the same flight for the same person from 2 different TA's. A few days LH called me and said my bookings would be cancelled as there was an "illegal double booking". It took me about a day to sort this out but beware that airlines don't seem to like this.