I totally understand that. My parents are in the same condition and I am their primary caretaker. (My mom has MS and my dad has Parkinson's). Since your sister uses part-time helpers, is there any way the helpers could be involved in arranging a visit? I would never let my parents attempt to go somewhere on their own, but I frequently take them out under my supervision or have one or the helpers do so. Would the helpers be willing to help you see them? Perhaps your sister would more amenable to that since someone she hired and trusts was there with you the whole time (but not her)?