hey hey salden06
where are you flying from? know that check in times to hotels/apartments are usually 3-4pm, unless your get approval for early check in or rent an extra day. if early and jet lag, where you put your luggage unless place has place to store luggage before check in. how tired and jet lagged will all be if flying from far? have you been before?
airbnb.com look for places near san marco, which is a very crowded area & busy place, how many beds unless a sofa couch which is not the most comfortable.
booking.com look for hotels/apartments that you will need, use filters on left side.
what is your budget in euros? what dates are you planning? it is high season, will be crowded, places are much higher during summer season and you have 5 people. many hotels have 2-3 max per room, since the rooms are small, and city ordinance
figure what transportation you'll need to get to venice/accomodation. pack light, everyone in charge of their own bags, many steps/bridges/stairs to climb up/down/over
europeforvisitors.com
lots of info here, what do you want to see, have the kids involved with a short visit. good luck happy travels
aloha