Unfortunately, the only way to assign the credits from each dependant to different parents when using the TurboTax CD/Download version is to prepare your tax returns separately.

As this version of the software will claim the amounts from both children on the same parent, you will have to prepare the parent returns separately and each parent will claim only one dependant and the tuition transfer from that dependant. 

If you are using TurboTax Online, you can assign the tuition from different dependants to different parents in returns prepared together. After entering the dependant information, in the Claims for Dependants - Tuition Transfer section, after you enter the information, you will see a box at the bottom of the Tuition Transfer screen, click the button titled Tuition Transfer and you can choose which parent you want the Tuition Transfer to appear on.