This does sound so painful and sad. I have personally not had any issues in my family with the elders passing as there was nothing to fight over. However, I was trustee and executor for wealthy clients. The trust attorney was very astute in setting up the complicated structure, making the grands wait for 5 years before principal distribution. That cooled some heels among them but there was antagonism towards me as trustee.
When questions or complaints arose, I simply pointed to the trust a copy of which they had before death. There was also a private letter for some property distributions with one item creating an issue - so I donated it.
As Lion said, breathe, hang in there, do what is right, vent here, and know you have done your best to care for your mother and abide by her wishes.