For people who like rice but not fish, serve vegetarian makisushi (simple rolls). Common vegetarian ingredients include avocado, cucumber, and plum. You could also use cooked chicken or beef instead of fish, though at that point your food is becoming more Japanese-inspired than Japanese-- by which I mean that I've never seen "grilled steak maki" served anywhere in Japan.

For people who can eat neither rice nor fish, why make it difficult by trying to feed them sushi? Sushi is not the only style of Japanese food. Serve an izakaya style dinner with a variety of dishes such as yakitori (grilled meats on skewers), udon noodles, agedashi tofu, and Chinese dishes such as shu mai and gyoza, in addition to sushi.

The main point it, don't get hung up on creating facsimiles of fish and rice. A vegetarian friend of mine observes that the worst vegetarian food is the stuff designed to look and taste like meat. As if all vegetarians are secretly craving bacon! For your guests who dislike rice and fish, look for other Japanese foods they will like, or find ways to serve the food they do like with Japanese ambiance.