How would you prepare this recipe for six or eight people?

Definitely the chicken should remain on a single layer for best textural results. On the one hand, you might be able to get away with browning/roasting the elements in a really hot oven (425°) on a sheet pan, but to reduce the sauce, higher sides would be helpful. And you want the cider and stick to relate to the chicken drippings as they cook. I second that you could cook this in batches, in advance. Chicken thighs are very forgiving in that way. And as long as you use firm, tart apples, those elements won’t fall apart for having been cooked earlier. I might store the liquid separately, so that the chicken skin can recrisp (face down in a cast iron skillet, or on a tray in the toaster oven). Let me know what you decide, and how it goes!

Disclaimer: I have not made this recipe (I generally don't follow recipes) although I've made many similar dishes.

This preparation is a bit unusual because it's a hybrid: an open braise/roast. The primary components need to be in a single layer since it's not a traditional braise with a lid to cover.

There are certain considerations. The recipe calls for four thighs, meaning one thigh per guest if it serves four, two thighs per guest if it serves two.

If you are scaling for 6-8 guests, you will first have to decide whether or not you consider one or two thighs a serving.

If you are cooking six thighs this shouldn't be too much of a burden, an extra-large cast iron skillet can handle the scaled quantity of ingredients.

However if you decide you are serving two thighs per serving for eight people (16 thighs), you will have to look at your available cookware. Something like a large heavy-duty roasting pan would be able to take the stovetop heat from two burners/elements and be large enough to accommodate 16 thighs, onions, apples, etc. In a restaurant, they might use a large rondeau but most home cooks don't have one: the Dutch oven might be the closest thing they have.

Depending on your stove and available cookware, you may need to brown the chicken in batches, removing them, and then working on the onions and apples.

The key is to make sure the chicken is cooked all the way through. If you have two separate batches, you can combine them before serving so the flavor is balanced. If one pan finishes sooner, pull it out and let it rest until the other batch is fully cooked.

I will note that this dish looks like it could easily be prepared in advance and reheated for serving. In that case, I might consider separating the chicken from the other items and reheating them separately.

I've actually thought about this exact question for dinner for 6. This doesn't exactly reduce the PIA factor, but I'd brown the chicken parts and place them in a large baking dish; brown the onions and apples; add the cider, thyme, seasoning and broth, boil that down, then pour it over the chicken parts, scooting the onions and apples where I could in the baking dish. It might take longer to cook this way--maybe 1/2 hour or so--and you want to make sure that the browned chicken skin is above the level of the liquid so it stays relatively crisp. I hope this helps.