I donâ€™t understand Robins Silverbergâ€™s math. The difference of $200,000, if correct, divided by 4 is $50,000. After any kind of normal commission, that is a lot more than $7,666.
From the facts you stated, your sister is not looking after the best interests of all of the beneficiaries of trust. If you believe that is true, you need to seek a legal opinion ASAP. Fighting the trustee of a trust may cost more than it is worth. Find out before it is too late.
As I mentioned in my answer to your first question, the loan company needs to know that they are dealing with the right person (trustee) who does have the power to make decisions on behalf of the trust.