I'm not sure about the # in room restriction, but we stayed at Hilton Garden Inn (a fairly new property) just off Merriman (Smith Road, I believe) and it was lovely.
We opted for a park and fly room at a rate of $129. It included 10 days parking (either in the hotel lot or a commercial lot, your option). We added two days parking for $10 since we were going to be gone 12 nights. Initially we were going to park at the commercial lot, but when we saw the facility, we decided it would be more convenient to leave our vehicle at the hotel.
We've also stayed park and fly at Courtyard by Marriott--also a decent property, but it included fewer parking days for the same rate as Hilton. Hilton also has a suites hotel which might be an option for your family of 5.
There used to be a Fairfield Inn, but I believe it's now Ramada that has a park and fly. La Quinta was also reasonable as I recall when I checked. Do NOT, under any circumstances, book a room at Clarion on Merriman--it was an absolute PIT!
We always fly on one of the first flights out of Detroit and all of the hotels we've stayed at begin the shuttle service at 5:00 a.m. or are 24 hour services. Further, you always have the option of waiting to park, at a commercial lot, on your flight day. The shuttles at the commercial lot included with our park and fly package run 24 hours.
Happy hunting!