There comes a point where you can’t internalize anymore, it isn’t healthy for you. These self-centered individuals need a wake up call. Unfortunately they probably aren’t putting two and two together, are still in denial. Your time is worth something too. So if your BIL isn’t contributing his time and energy, then he needs to contribute more financially. In the end you will have no regrets, you did what you could to inform them before, and you did what you could to help after their poor decisions. I am sure your FIL has regrets now.
There comes a point where you can’t internalize anymore, it isn’t healthy for you. These self-centered individuals need a wake up call.