Unfortunately not, there are is no Milford Sound and Doubtful Sound package. That's ok though, you wouldn't be able to see them properly in the same day anyway. If you want to see both, I'd recommend basing yourself in Te Anau and booking separate tours that leave from there. You can book a Milford Sound tour coach to take you to Milford Sound and back for one day and then a tour of Doubtful Sound the next day.