[AC Question]

Stupid question I just got the Galaxy S5 how do I send specific few contacts straight to voicemail without blocking them completely and allowing them to know that I did this as well also want to be able to hear the messages that they leave if any until I'm ready to take them off vmail forwarding and talk to them this is what I would like to do please help if possible.. I can't find accurate answers for the current phone model online thanks