Help with a partial tur-duck please

If they are separate, or separable, I would roast them individually, as they need to go to different temperatures to be all of safely cooked, tasty and not dry.
For ex, if you roast to get prime quality turnkey, duck will be undercooked. And if you roast to get prime quality duck, turkey will be dry.
If that's not possible, roast the combined meat until the turkey is ready, remove from oven and then cut off the duck and return to finish roasting.
See this article from Serious Eats a few years ago about these roasting problems with the recently classic turducken, and a roasting chart from Thermo Blog for individual meats.
https://www.seriouseats.com/2012/11/the-food-lab-the-ulimate-turducken.html
https://blog.thermoworks.com/thermometer/chef-recommended-tw-approved/