For family-friendly and beach, perhaps look at some of the towns in Michigan on the beaches of Lake Michigan.....can't think of names of town at moment, but look at towns on the lake in Michigan just north of Indiana border. Some are known as the weekend retreats/2nd homes for Chicagoans living on Gold Coast. Should be some rentals of luxury houses within walking distance of beach, and an easy drive from Chicago.
Aiming for the luxury of having family all together without wasting a lot of travel time & hassle can outweight pure luxury surroundings. When we rent a beach house we bring our own fluffy towels and better sheets, plus plenty of hotel soap and it's nice......easy to do when driving!