Unfortunately, even cutting out the non-essentials I really can’t make ends meet and pay down debt and save if I don’t have some sort of even minimal contribution from her that she’s making right now. As they say it’s better than nothing…
It’s really awful that I’m even having to make these decisions. It really does hit for me how it’s more like I’m dealing with a child than another adult.
But at this point I 100% do not trust that if I passed away, and my wife got the substantial life insurance on me that there would be anything left in Five or 10 years, let alone when my son would need it later in life
I want to address these aspects of your post- in the hope that it will give you some ideas of how to best prepare for your son one day but also not just your son, but for you, your wife, and, the impact of the preparation- or lack of- or the potential financial and emotional effect of these dynamics on your daughter.
That your living expenses are in a situation where you need a contribution from your wife is concerning, because it relies on an unreliable person. I learned even by my teens to not rely on my BPD mother for anything. There are emotional aspects to money. One is power and control.
That you need her money for your combined life style puts you in a precarious situation. It may seem ludicrous to suggest that you make changes to live on your income alone-but it's a way of maintaining control of your own money and future and this makes a difference. Changes like this can not be done quickly. Start with what you can do. The obvious one is the fancy dinners out. It's not sensible to do that when in debt.
With a person who has NPD, controlling you with money puts them above you. Asking BPD mother for money (Dad earned it, but she controlled it) would give her license for humiliation and control. You would be "less" in her eyes. In your situation, you are a main contributor but the emotions, power, dynamics- with a BPD/NPD person aren't logical.
You can not control if your wife contributes or not. The natural consequence of her not doing this is that the family lives on your salary alone. It may not be fair (but fair isn't a consideration here) and your wife won't like it but this is what happens with money: if one's expenses exceed income- the money will be gone. It's better that your wife learns this now, because if this were to continue- the possible circumstances of two elderly parents in need, and a brother with special needs could fall on the shoulders of your daughter, who also may have her own family needs to consider at the same time.
What do you want for your daughter? Out of all of you, she is your least concern and that's good for her, but emotionally she still needs to know you care about her, even if she doesn't need your money. It also appears she has a moral core and won't let her elderly parents or brother lack basic needs but she also may have her own family to care for too. You've mentioned your concern for your son, but what about your daughter? While it's important to plan for your son's needs - it's also important to plan for yours (and your wife's should you stay together).
I was concerned that BPD mother would go through her money too quickly and then not have the savings in her own time of need. We would be willing to help an elderly parent who, through circumstances they could not control, was in need. This was different though. She did not have need. Her spending was the issue and she was keeping her own finances secret. While she didn't ask us for money as long as she had hers to spend- we were concerned about her running out. We didn't know how serious her circumstances were until we found out by accident that she had leveraged the equity in her home, and had few savings left.
She would not cooperate with any plan to be transparent, to budget. Asking her about money led to her accusing us of wanting it. I could not be involved with her finances if being accused of this. So when another reliable relative offered to help her with a budget- I was relieved. She agreed at first but then changed her mind.
The best gift my father left his children was not for us but for her, and it was one I was thankful for every day. He had put some of the money into a fund that paid a monthly sum which was sufficient to meet her needs. Eventually BPD mother allowed me to access this to cover her bills. However there was stress and drama and power struggle over what was "her money". While I had wished my parents had allowed me to help manage it earlier to avoid a financial crisis, I realized there'd be more of this, and it would not have been effective. I had no legal power over what she did with it. There was no way to control her, she was going to do what she was going to do.
Consider this idea when you plan for your savings. Such funds may come with different risks/benefits, so they probably should not be the entire of the savings but one also has to consider the circumstances and behavior of the person who has access to the funds. I am not a financial advisor but I think it's wise to work with one for planning for your circumstances.
I think it also helps to have a third person to point to as the decision maker with your finances. Rather than say "no more fancy dinners" it's "financial advise is to stop the dinners". It takes down the emotional aspect of the money decisions.