I'd recommend looking at 'kids eat in colour' on Facebook. I go with a division of responsibility approach, I provide the food and its entirely up to my kids whether they eat it or not. I always provide something on their plate which I know they like and something new or which they didn't eat last time. With 'fussy eaters' it's best to diversify their diets not contract them. If they'll only eat a handful of foods them add more different things for them to try, it doesn't matter if they eat it or not. Exposure is the key. Tastes change over time, my 3yr old has just decided he likes beetroot and will only eat mushrooms at nursery. Snack plates are great for exposure, put small amounts of lots of things on a plate and just let them eat what they want as snacks during the day. If you ask you for food just point them to the snack plate, if they've eaten all of something maybe refill. I'd recommend you eat everything you give to them and eat with them at a table or on the floor as a picnic as a group.
*by snacks I do not mean just sugary, salty snacks, I mean essentially finger food - it could be biscuits, cheese, ham, pepper, tomatoes, cucumber, raisins, nuts, cream cheese and breadsticks, fruit, pasta, chicken, yoghurt - think all the nutrition in snack form.
My eldest son has always been a fussy eater but now diagnosed with autism my youngest eats most things and is neurotypical.