I think you would have to change color to the correct characters each turn when it's time to select cards, pick their cards, and move on to the next.

you have to play with open hands or change the color each time, sorry

On the far left hand side of the TTS UI, where there are icons running down the side, click the third one down for the Zones tools, then the middle icon for the Hands tool.

You should see coloured squares representing the spaces for each player's hand zone. Right click on the zones you want to control, change them to your colour.

This might break some auto setup and auto scenario ending features where they return cards for the extra player, but you can manually put them in the hand zones.