Looks like you've got lots of great advice here. As usual I'm thinking like Andrea that it also sounds like a bit of hectic household (and why not there's a new BABY & everyone wants to meet him ) so really A LOT has changed for Jack. He's definitely not used to this highly social environment & with strange things come strange B noises
Here's what I would do:
1-I'd get this great book by Pia Silvani on Puppies & Kids. There's lots of great advice there.
2-Find a quiet room..away from the guests & ESPECIALLY any children guests that can be dangerous :eek: Spend some time with Jack just one on one in his new safe place. Bring him yummy treats (like a rawhide or a hamburger or a pigs ear YUM )
3-If he absolutely must be loose around the house then I would make sure that I am there at ALL TIMES…no if's and's or but's about it. If I'm not there then neither is Jack. It's MY responsibility to have to manage the situation & if I can't be there then the dog must be put in a safe place where he's not stressed out & afraid.
4-If I'm with him then it would work like this:
-When Jack approaches someone growling...the person should fold their arms look away & turn your body away from him (never stare at the dog when they're growling) & ignore him. There are lots of calming dog signals in this behavior.
-When he stops growling..."GOOD BOY...bacon, beef, chicken treats"
-If Jack gets anxious at people's movements then practice his sit & downs...ask Jack to SIT & if he listens then it's.."GOOD BOY..treats treats treats" and then the person can get up & move.
-If Jack gets anxious while people are eating...then you divert his attention call him over to another place have him SIT & then it's..."GOOD BOY..treats treats treats"
-If you have the baby & Jack gets anxious ask him to get into a DOWN & STAY..if he does it then it's..."GOOD BOY..treats treats treats"
It's all about re-asserting yourself as his protector. It sounds to me like the situation is making him nervous & afraid. The more you work with him that there's nothing to worry about the easier it will be for him to relax & calm down.
I realize you have a new baby & it will be hard to manage both Jack & the baby maybe DH can help or maybe your mom can help but if you can't work with Jack then your safest bet is to find Jack a safe place in your home.
Good luck!