Sadwife so very sorry to hear about your sister and her baby. very sad indeed. I will be praying for her and your entire family.
The father sounds like a problem because instead of helping his advice and well intentioned (although ignorant)suggestions only seem to exacerbate the problem.
You seem very clear headed and have a good plan in place. I hope you can find either a good support group or at least individual therapy that can help you. You shouldnt have to face this alone. Hugs.