When you represent yourself, you typically do so at your own peril. There are rules that need to be followed. Your evidence of the property's value would need to have been corroborated and/or you should've had the appraiser there to testify concerning the methodology used to arrive at his appraisal amount.
To answer your specific question, based on the information you provided it is difficult to opine whether these 3 people are "disinterested parties." You might have had to object to their being on the commission at the time of the hearing to preserve this argument. Did these people disclose their employment or other pertinent information at the hearing?
If this is important to you, you should consult an attorney asap. You may have time within which to file an appeal and/or show that the commissioners weren't impartial, if you suspect that they weren't.
DISCLAIMER: Brandy A. Peeples is licensed to practice law in the State of Maryland. This answer is being provided for informational purposes only and the laws of your jurisdiction may differ. This answer based on general legal principles and is not intended for the purpose of providing specific legal advice or opinions. Under no circumstances does this answer constitute the establishment of an attorney-client relationship. For legal advice relating to your specific situation, I strongly urge you to consult with an attorney in your area. NO COMMUNICATIONS WITH ME ARE TO BE CONSTRUED AS ARISING FROM AN ATTORNEY-CLIENT RELATIONSHIP AND NO ATTORNEY-CLIENT RELATIONSHIP WILL BE ESTABLISHED WITH ME UNLESS I HAVE EXPRESSLY AGREED TO UNDERTAKE YOUR REPRESENTATION, WHICH INCLUDES THE EXECUTION OF A WRITTEN AGREEMENT OF RETAINER.