So you have 2 adults (1 bitch / 1 dog) and the 6 month puppy.
Is that right ?
If it was me, i'd be keeping them together in the same room but with a decient distance between them if you know what I mean

Let them eyeball each other. If one starts then slap it down a little then reward the other one with a treat

The naughty one will soon get the message of whats right and wrong when one dog gets a treat and he doesn't.
Always walk them together BUT keep them at a long arms distance apart for a few months. If one starts, use the above method.
For some reason, the male has got it into his head that the pup is a threat to his position.
Had a similar thing with my daft mutt.
4 years ago, a black lab growled at my lad who was rideing his bike at the time.
Daft dog jumped between them and stuck his face into the labs face.
The lab made the mistake of snarling back so daft dog really knocked him about (which wasn't a real problem because as far as I was conserned he was just protecting my lad)
The real problem was that everytime he saw a black lab after that, he dived straight in and had a bloody go at the inocent dog

The only way we cured him was to keep him on a lead when we saw them and push them together until he reliesed that every black dog wasn't a threat

If he started, he got a slap and the other dog got a treat off me
It took about 6 months but it worked

Cost me a bloody fortune in treats too

I've no problems nowdays.