10 lb pork tenderloin and 10lb brisket

I'd go a little lower if your going more than 6 hrs. If your oven is big enough I don't see the problem of putting them both in there.

First it's a pork loin not a tenderloin. If you have a ten pound tenderloin that's a huge arse pig.

Second it's a very lean piece of meat not needing that prolonged cooking. I cook them rather quick and cook to medium which makes them stay moist.

That said, if for some reason you do want to cook them that long I see no reason why you can't put the two together. The pork should have some liquid to braise and keep from drying out.