How do I get my dog to stop barking at everything?

Background:

I have a 4 year old German shepherd, husky, pointer mix who’s gone completely haywire recently. He’s a rescue and overall has been a great dog in the 3 years I’ve had him. He’s responded decently well to training, although he’s pretty slow to pick things up and retain. He’s the problem child I’ll be talking about.

He is bonded to my other dog, a 6 year old cattle dog/coonhound/pitbull mix, who is the sharpest, smartest dog I’ve ever had the pleasure of working with. My pitty mix has always been a huge help with my German mix and will remind my German mix of boundaries and expectations frequently (biting his legs to get him down when he stands up on the dog gates, pushing him to the side when he’s not paying attention to where the baby is, things like that).

I also have two cats who have been raised around my dogs. They all coexist and love on each other all the time. My dogs have always treated the cats like their puppies and will gently correct bad behaviors, play with them (usually pups laying down and the cats will run around them and tackle them), and will come running if my cats sound like they’re in distress.

I’ve worked extensively with my dogs to train them. I’ve used positive reinforcement, ignoring attention seeking barking, distracting from triggers, confidence boosting, recall, etc. They work with me around my horses so I’ve needed them to be well trained.

The issue:

Recently, he’s been really bad and has started regressing in his training despite me being consistent in commands, rewards, and exercise. He chases the cats, has recently gone after my younger cat (didn’t hurt her or really put much effort into hurting her, but I couldn’t really tell what his intentions were), and he barks at EVERYTHING. It’s driving me nuts. I can’t figure out what’s happening. Car drives by? He barks. People talk outside the door? He barks. A squirrel goes by? He barks. Delivery man walks up or someone knocks? He goes berserk. He’s starting to make my cattle dog/pitbull mix regress in his training too. I’ve never seen my dogs act this way. It’s gotten to the point where my daughter has been refusing naps because he barks so much while she’s asleep and it wakes her up.

The only thing I can think of that’s changed (and a pretty big change too) is I’m pregnant with my second baby due in January, and my toddler has started walking and being more active with the dogs. They’ve been nothing but gentle and sweet with her though, so I don’t know if it’s just anxiety around protecting her or stress? I’m at my wits end, someone please help me.