Hi dtkm;
What a frustrating situation. The "rules for you but not for me" mentality gets old pretty fast -- I understand

Double standards would make anyone want to scream!
Some parts of the situation sound like "quick wins" or "low hanging fruit" for a solution. Other parts sound more challenging to figure out.
Fortunately, you won't have to get his cooperation or agreement, or get him to see your point, or have him think your solutions are good ideas, for you to try them. I can't imagine trying to convince a pwBPD that the rules should be the same for both of you -- a losing proposition for sure!
Let's take a look at this:
Since Saturday my uBPDh has either been in a bad mood or nat talking to me for who knows why…cause my son had basketball games that were canceled because of the snow or because I had mentioned trying to work on Monday’s…?? Your guess is as good as mine.
This looks like a "quick win" to me. He is allowed to cope with life by not talking to you, and he is allowed to have irrational reasons or unknown reasons to do so. That doesn't mean it's a functional coping mechanism -- but he controls how he responds to life.
Can we reframe this as a break for you. You get a break from interacting with him, and you can give yourself permission not to try to figure out why he's in a mood. His mood may actually have nothing to do with any rational external event. All the energy that would've gone into focusing on his mood and wondering why he's in a mood... can you do something nice for yourself instead, while you get a break from him talking to you?
He literally will not speak to me or my kids, his step kids. Throughout this time, my kids and I have all been very cordial (a lot has gone on like I had to take our cat to the emergency vet and in the middle of that the school nurse calls as my daughter needs to come home since she is sick and he didn’t offer any help or ask if either were ok). We have said hi and bye as we are mandated to do by him. He will not respond to any of the 3 of us. He says hi/bye to all but the 3 of us. (As a side note, my stepdaughter left on Saturday to go to her moms without saying bye to any of us and none of us but my husband knew where she was…including the 3 year old).
This is hurtful behavior that isn't under your control. This is kind of just who he is going to be. It doesn't matter whether you and the kids always said Hi and Bye to him 100% of the time, that won't impact whether he interacts with you or not, because his feelings and motivations come from inside of him, not from anything you and the kids say or do "right" or "wrong".
What is under your control is whether you consider it behavior that you can live with. Maybe it could help to look at four options:
You consider it behavior you can live with, and stay, but remain frustrated by it (Conflicted board)
You consider it behavior you can live with, and stay, and find a way to depersonalize it (Staying/Bettering board)
You consider it behavior you cannot live with, so end the relationship, but remain frustrated by it (Detaching board)
You consider it behavior you cannot live with, so end the relationship, and find a way to depersonalize it (Detaching board)
There are no right or wrong answers -- only what you decide for yourself is OK to have in your life. Everyone's boundaries for what's livable are different.
Probably the most frustrating position to be in, though, would be staying in the relationship with a leaving mindset.
...
It is concerning how he treats the kids.
Can we come up with some boundaries (rules for you, not him) that would protect them from his hurtful behavior?