It seems like you and your family are punishing Mack only halfway. When you verbally reprimand him, do you ever dole out consequences? If not, Mack knows that if he persists enough, he'll get what he wants. In the same sense, even negative reinforcement is positive reinforcement in this situation. Mack wants your BF and so nips and barks at him. BF says No and I would imagine probably started swatting Mack or some similar action. That, in itself, is positive reinforcement for Mack to continue nipping/barking.

Instead of arbitrarily rewarding Mack's behavior, do NOT give any reinforcement whatsoever when he is doing an undesirable behavior.

For nipping, you have two methods:

1. When puppies were young, they learned bite inhibition through each other. Whenever a littermate bit too rough, the pupppy would yelp. The rule was simple: play nice or leave. You can mimic this by yelping "OUCH!" loudly every time Mack bites and if he backs off or sits, praise and treat. And, if desired, you can shove a chew toy in his mouth.

2. Give absolutely no reinforcement when Mack nips. When he nips, stand as still as a tree with your arms crossed. You should even look the other way because staring a dog in the eyes is exciting to them. When he backs off or sits down, praise and treat.

For the barking, ignore it altogether. No reinforcement = no purpose to continue the behavior. Keep in mind, there will be what is known as the "extinction burst". Because Mack has been so successful with his barking, he will continue doing it. Thus, when you try to ignore his barking, he might possibly increase his barking because he thinks you'll give in. Just keep ignoring him and he will stop. Good luck!

ETA: I also wanted to add that now would be an excellent time to start Nothing in Life is Free (NILIF). With this training method, the pack hierarchy is established as you being the alpha and Mack the subservient member. This will help you IMMENSELY as you try to control his behavior:
http://k9deb.com/nilif.htm
http://www.greyhoundlist.org/nothing_is_free.htm