Is sauerkraut a tradition in your family? I grew up with it but I don't generally see it as a crowd pleaser. And if it is then you need the mashed potato because the two together is the perfect bite.
What about roasted red potatoes? You can roast in olive oil, garlic, and parm cheese.
For more color butternut squash is also very good. My mom made it at Thanksgiving with lots of cinnamon and a tiny bit of maple syrup. I swear it was amazing.
I feel like that might be harder to do for 16 people?
Mashed potatoes are a lot easier than roasted if you're short on oven space.
I like to make them with red skinned potatoes. Peel a bunch of garlic cloves and throw them in with the potatoes while they cook. Mash with butter and cream or half and half.
How are you making the Brussels sprouts? 16 people is a lot if you only have one oven - I try to write out how I'm going to time it (do you have roast resting while you cook green bean casserole? Is there room in the oven for both at once? Are you sauteeing or roasting the Brussels sprouts?)