Sorry, this is not an immigration question.
IMMIGRATION LAW PROFESSOR for 10 years -- LEGAL DISCLAIMER: This answer is offered for informational purposes only. It does not constitute an attorney-client relationship.
You should consult with an attorney as quickly as possible. If your mother has Alzheimers and your dad had a stroke, this may be a case of financial elder abuse by the travel agent.
Legal disclaimer: Information contained herein is not intended to and does not constitute legal advice nor does it create an attorney/client relationship.
If your parents are mentally competent, then you cannot help the fact that they are making poor decisions. If your parents are not competent and not able to handle their financial affairs (and that is what it sounds like from your inquiry), then a conservatorship is appropriate to protect them from being taken advantage of. So not sure why you say a conservatorship "is not quite what needs to be done."
This answer does not create an attorney-client relationship between the person posing the question and the attorney answering it. If you need further legal help, please retain and confer with your own counsel.