How to cook Brussells Sprouts and sweet potates in one oven?
I have this problem frequently of needing to cook different things at the different temperatures in the oven at the same time. I tend to get around it by choosing the average temperature of the two (in your case ~390F) and adjust my cooking times appropriately. At 390F, I would cook for roughly the following times for your foods:

Brussels Sprouts    35"
Sweet Potatoes      70"

They should could in a pretty similar manner to your recipe, but I'd keep an eye on them to ensure they come out perfect.

Hope that helps!

Mike