And how do they sign the transactions?
Like normal addresses. Assume there are 6 staff and you need at-least 5 staff to approve the transaction. You create a 5-of-6 multisig address. This is how you create a transaction:
#1: Staff-1 create a transaction and sign it with his/her key.
#2: Staff-1 sends that signed transaction to Staff-2.
#3: Staff-2 signs it with his/her key and sends the signed transaction to Staff-3.
#4: Staff-3 signs it with his/her key and sends the signed transaction to Staff-4.
#5: Staff-4 signs it with his/her key and sends the signed transaction to Staff-5.
#6: Staff-5 signs it with his/her key.
#7: Staff-5 broadcast/push the transaction.
If you want all(six) staffs to approve the transaction, then you create a 6-of-6 multisig address. If you do, there will be a slight change in steps.
#6: Staff-5 signs it with his/her key and sends the signed transaction to Staff-6.
#6: Staff-6 signs it with his/her key.
#7: Staff-6 broadcast/push the transaction.