Having a guest who is "sort of" kosher. Since fish is, I believe, neutral under kosher rules, a fish main course would give me more flexibility for appetizers and dessert.
I have an easy Provencal fish stew from Pierre Franey that I have made many times, but when I adapted it without scallops, it ended up tasting too fishy.
To complicate things, another guest hates olives and has trouble digesting anything spicy. So, sauted fish topped with sauted cherry tomatoes, onions, garlic & black olives, a favorite preparation of mine, is out. I don't love poached salmon and broiling makes the house smell.
Other than fish stew, I'm thinking sauted halibut with an interesting sauce. If not a stew, stovetop grilling or saute seem the best prep options.