I'm guessing with the number of people you are talking about, it's more likely to be a cocktail party with hors d'oeuvres and not a meal with appetizers.
For an appetizer at a sit-down meal where utensils are available for use, I really like something like a baked goat cheese with crostini. Hot crab spread would be a second choice to spread on toast points or plain crostini. Ceviche is also nice as an appetizer. Samosa can be easy if you use wonton wrappers. Honestly, it would mostly depend on what you are serving for dinner, and the theme of the dinner.
For passed or stationary hors d'oeuvres, at a cocktail party where people don't have a place to sit and use utensils (and dinner won't follow as with appetizers), I like to serve foods that are dough-based (and more filling). Usually, I use puff pastry or phyllo dough for the base, in mini muffin tins or tiny tartlet shell tins. You can fill them with anything from seafood mixes, onions and cheese, chicken salad, etc. I also really like to make-ahead a variety of cocktail breads (I like thinly-sliced french baguette) with various toppings. Because this is an hors d'oeuvre, I make the combinations myself ahead of time, so people are not trying to assemble them without utensils. Some suggestions: lox, cream cheese, capers; crab salad topped with finely diced tomatoes and fresh dill; boursin cheese, basil, tomato; provolone, thinly sliced cucumber, parsley leaf; cream cheese, roasted red pepper, balsamic drizzle. For dessert, I always do a variety of baklava served in a mini muffin paper cup. All of these are, at most, 2-bite, as hors d'oeuvres should be.
The sky's the limit. It just depends on if you are talking about appetizers or hors d'oeuvres. I can't imagine doing a dinner for 100 by myself. I hope you have help! Good luck!
) That way, your time can be devoted to your brother! 
