Smoking temps are the same no matter what you're working with for meat; it's the TIME in range that makes the difference.
I'd also put the turkey below brisket as you don't want nasties from the bird dripping on your brisket (which will probably take about 3 hours longer than the bird & will get wrapped - & in my case coolered for the long term warm down). - for a lot longer than the bird might.
Then maintain similar temp ("smoking" range on your thermometer) & put the brisket in first. When you're the appropriate amount of time away frorm how long it would take to do the bird, insert it to the smoke chamber.
I suggest allowing about 5 to 10 (max) minutes for getting back up to temp & of course, the smoke chamber door is open as short an amount of time as possible.