Roasting beef and lamb roasts together
I used to cook lamb (when I had to). I never cooked it with anything because the "lamby" flavor tended to transfer. Mutton, on the other hand, tastes a lot like mild beef, so I did cook those together. All I can suggest is that if you want to cook both in the same roaster, put one of the roasts into an oven bag to keep it separate from the other. There will be a modest transfer of aroma, but not of taste.