The hotel vouchers are very simple. When you get newark, speak to the customer service agent that meets your flight. The voucher will name the hotel, it will most likely be one of the airport hotels that has a free airport shuttle. If it dosesnt, ask the airline for a taxi voucher. When you check-in, just give the hotel the voucher, and you're done. You'll need a credit card when you checkin , to cover incidental charges, like room service and the like. You won't be charged for the room.

You should also ask for meal vouchers, they'll probably be given with the hotel voucher. Since your overnighting, you should get both a dinner and breakfast voucher for 3 people.

Since, you're on a mileage ticket, the airline has no obligation to put you on another airline. It doesn't hurt to ask, just don't expect to get it.