Yes, you can use 2 vouchers in one day, but you will most likely need a supervisor override as the PP mentioned.
I'm guessing you have ten people in your group? You may be able to receive 10 FP cards for your group for each voucher. Disney states that you may receive up to six FP cards per voucher, but people have reported getting more (I remember a specific report of someone getting 10 FP cards). Everyone will have to have a valid ticket, and you must have all tickets there when you turn in the voucher (i.e. you can't get a FP card for someone in your group who is sleeping late and is not with you at the time of redemption). Disney policy states everyone must be present, but people have been successful having all tickets at Will Call with everyone present in the general area (putting on sunscreen, etc). All ten of you don't need to stand in the Will Call line together.