If we use the full service Live Premier option to file returns for two people, what is the total cost?

I don't know how you arrived at a total cost of $260. The prices I see on the TurboTax web site right now are $170 for TurboTax Live Premier (federal) plus $55 for the state, which makes a total of $225.

In any case, the cost is per tax return. If the two people are married and filing a joint tax return, then the $225 or $260 is the total cost for both people. But if the two people are each filing their own separate tax returns, then they each have to pay that amount.

There is also an extra $40 or 45 if you want to have the fees deducted from a federal refund.