As to cancelling a PS, yes it is OK to do so the day of and in fact it is highly recommended that you do so if you know you are not going, so someone else can get your time. As to your husband not liking anything too fancy or too pricey, we can help with the not fancy but at WDW it is hard to help with the not pricey as even a cold coke at the outdoor stands goes for $2.50. As far as what PS's you need -- during that time of year make them well in advance for dinner and character meals at the parks. Resort restaurants are generally still easy to get by just calling the day before. You can even get many park restaurants that way but often your desired time or anything near it will not be available. Exception for Easter Sunday -- definitely reserve well in advance to eat anywhere at WDW.
Most restaurants at WDW are not too fancy -- well-themed but very informal (shorts everywhere except Victoria and Albert's at Grand Floridian which actually requires jacket). And just about everywhere you go will have lots of kids present. Much depends on kind of food you want , and whether you desire a buffet or be served at the table. Some of our favorites are MK: Liberty Tree Tavern for dinner -- character meal (American fare) served at table, revolutionary time naval theme; Crystal Palace -- buffet (character meals), very impressive decor. Epcot: Japan Teppanyaki restaurant, sit at table of 8 where cook prepares food right in front of you; Germany's Biergarten, German buffet, liter size steins of beer, Oktoberfest band in the evening with sing-along and dancing (perhaps least costly of Epcot restaurants, which are all expensive); Mexico's San Angel, little bit more fancy than others, expensive but good Mexican food and powerful margauritas; Canada's Le Cellier (means in the basement and that is where it is), very informal, steak restaurant. MGM: Hollywood & Vine -- very informal buffet resataurant; Mama Melrose, decent Italian. AK: no real sit-down restaurants there except Rainforest chain restaurtant which I avoid like the plaque. There are also many good places at the resorts and Downtown Disney.