OP, kindly, I wonder why you think you have to carry all this? What would happen to you if you didnt have BiL over? Would you be arrested and put in "bad SiL and bad aunt" jail?
I assume you are very wealthy to be able to support these people financially. (Did you mention supporting your dps too)
But you are impoverishing yourself emotionally and are completely skint in that direction. Just because you and your dh want to be generous financially does not automatically give you the emotional and psychological resources to DO all this as well. You seem to have very little in the emotional bank.
I really think you would benefit from some therapy to understand why you feel the need to pour so much of yourself into these relationships when theybgive you so little back.
Your neice for example needs to grow up and make her own choices about her dad. You might not like what she decides (ignoring your bil completely, fir example) but that is her choice.
Have you always taken on everything for everyone?
STOP. YOU DON'T HAVE TO DO ALL THIS.
If you didn't have the money, what would happen to them all? (No need to answer - I just want you to think about it)
Much love, Christmas will be over soon 👍