Ok, it will be okay. You have shown us that you posess the crazy basenji mom traits that are needed to have a great basenji.:D
Caesar (my 5yr old basenji) never growled until I added the puppy basenji to the family. 5 years, no sounds of discontent ever. Keep in mind, that although basenjis dont bark, the do communicate through sound.
I found that (with basenji mom attention) Caesar's growling is innocent and is just his way of screaming about his space with Cairo when Cairo is bugging him and he doesnt want to move.
We hold his muzzle softly in our hands until he stops. We call it the growly old man sounds.
I think putting him outside may be the wrong thing. We all know our basenjis are happiest with us. I would suggest kennel time or the muzzle so that he is still in your sight and the bad behavior is being addressed until it stops.
I might suggest you push off your visitors a bit since Jack is expressing some serious stress. He sounds like he needs to adjust to the changes. I am sure you are not adjusted to the sleep cycles.
Have no fear or misunderstanding. He is just trying to figure out his place in the pack and if it has changed.
Also, keep reminding you and your husband that Jack's world is in your house. You are all he sees all day. Be patient and dont let yourselves be short and have Jack pay the price.
Dogs get jealous, mad, grumpy, growly and experience many traits that we have ourselves. I have seen Caesar lick little Cairo's eyes like a mommy and growl so loud at him in the kennel that it sounded like blood was spilling. There are all kinds of sounds they use to communicate. You now are learning some new forms of communication.
Determine what is okay, what is not. Address it. Always show your love. Your love for Jack is what has made him such a unique basenji. You will be fine and he will be your perfect silly boy again.
You can do this! You can do anything you put your mind too. You just had a baby! You can do anything.:)