OR .....
Statten ISland Ferry - beats the que for liberty island tour
Washington PArk, Grenwich Village on a saturday
Stay within a few block or either 8th Ave, 5th Ave from Spring Street to 110th and you are on the tube network really easily.
Cabs from JFK are expensive and with that luggage, 7 people your best doing a deal with Shuttle Bus firms. Its a $50 cab to manhatten island and you would need maybe 3 cabs......
Or the shuttle run at $15 a head. Try doing the Rock - The top of the rockafella centre, maybe a better view of the park and north manhatten, and the que is smaller than the empire state.
Macys is a cheap place to shop, but the other department stores on 5th avenue are over pricved. All the major brands have a shop in the city and a much cheaper, sometimes 50%, so itsw worth looking about first. Most designer brands are on Union or Spring Street. Thats the 6 car on the tube from the east side.