My sibling does not have my parents best interests at heart. What can I do to protect them?

My parents have just entered assisted living due to the early stages of Dementia. My sibling is trying to set up a Power of Attorney, and I feel he should not be alone on this document or not at all. I would like to be on the document. My reasons are around my siblings behaviour around my parents finances, belongings, and health needs. My sibling and his wife are looking out for themselves, and not of the needs of my parents. After taking advice, I have concluded that I should address this with the Social Worker. Speak with my parents before they sign anything. Ultimately I see my parents requiring decision making when they are not able, and for their welfare, i.e. clothing, health needs, etc to be addressed. I am very worried and anxious about causing problems in the family but I cannot see any other option given my siblings behaviour. My sibling 18 months ago, severed communication with me over a minor problem and in the last month has just re-opened communication. Ideally I would like to remain on good terms with my sibling and am treading on eggshells whilst getting more and more angry. I would really appreciate any comments, as I dare-say, this may be a common problem.