I would quietly go back on vacation and await legal counsel weighing in, and return from vacation a day or two after that dusts settles!
here is my concern - you (you being bank, not you personally) took action on something child A said verbally and provided, via screen shot, but won't take action on something child A said about filing charges:
"Child A sent over a screen shot of what looks like a patient portal page where a physician indicates, in the notes, that the customer/patient has dementia...and speaking with Child A"
"child A is stating that she is filing an Elder Abuse claim against Children B & C but it doesn’t seem to me that we can act upon her stating that she will be filing a claim."
Pretty much anything you do at this point just compounds the issue, so i would encourage legal to act quickly.