No, that’s not enough food.
My suggestion is to either get another turkey, or get a small ham or beef roast. Or serve another main dish that would feed about 6 people (for a group of a dozen). A lot of people like to have just a little turkey on Thanksgiving, but are delighted to see something non-traditional offered as well. I’ve had very good results with serving a (meat) lasagna alongside a small turkey, but most people like my lasagna at any time of the year. A nice big bowl of pasta and spaghetti sauce is colorful, and the sauce will be better if you make it a day or two before, and let the flavors blend. If you have a main dish that you’re proud of, go ahead and make it, just make the turkey as well.
Mashed potatoes are very traditional. You MIGHT be able to get away with just offering roast potatoes if you offer plenty of stuffing. MIGHT. But you’re going to need more stuffing than what you’ve listed. People like different kinds of stuffing, but everyone likes lots of it. You are also going to need turkey gravy, which you can make from scratch, from a packet, or just buy in jars. Again, you’re going to need lots of this. If you make the gravy from scratch, use a gravy separator, those things are great.
Do not fear the can of cranberry jelly. Just stick in the fridge until you’re getting stuff on the table. Then open it (preferably on both ends), let the jelly slide onto a serving platter, and slice into thin disks. Or you can use a small melon baller, and scoop out tiny balls which you place around the turkey on its platter. Some people think that the canned cranberry jelly is incredibly tacky, but most people LIKE to see it on the table, even if they don’t eat it. It’s part of the tradition. Personally, I like it, and I hate the cranberry relish that the foodies like these days. Your FIL was probably afraid that you didn’t realize the importance of the cranberry jelly. Or he’s a cheap bastard who thinks that he’s contributed to the cost of the feast.
Sweet potato casserole with marshmallows is also traditional. I prefer my sweet potatoes roasted, with a little butter and cinnamon and brown sugar, but a lot of people like the casserole on Thanksgiving. I don’t consider it essential, but a lot of people do, and your husband (or some of the guests) apparently does.
You will need at least another dozen rolls, possibly two dozen. Or make biscuits, which are fairly easy if you make drop biscuits. Cornbread, being very American, is also a good option. Jalapeno cornbread is very pretty, with red and green bits showing through the golden bread. I can’t eat it, but it’s very pretty.
My father regards a condiment platter to be essential for feasts. This consists of at least three kinds of olives, tiny sweet pickles, artichoke hearts, and peppercini. My mother and I insist on a raw veggie platter as well, which has things like celery, carrots, and bell peppers (use at least 2 colors), sliced, and broccoli and cauliflower florets, and halved cherry tomatoes, and green onions which have been trimmed, the outer two or three leaves peeled off, and the rest of the green sliced lengthwise. Plus we’ll put on whatever looks good from the produce section. Similarly, we assemble a fruit platter, and this is an ideal place for that sack of clementines, along with grapes and bananas and such.
I’d probably go with an apple pie along with the other two, and I’d add whipped cream to the options. However, I’ve never had pumpkin sorbet to offer.