What should I file to advise courts of my dads death if property in trust with 2 other family members?

My dad recently passed away and he was 1/3 owner of a trust set up by his mother to protect two parcels of acreage from ever being sold. When we contacted the brother and sister (the other two names on the trust), they indicated that they were going to sell the property and they had my dad sign a power of attorney a few months ago when he first became ill.
I realize that the power of attorney they had is now invalid- BUT, how do I contact the proper courts (I know deed #’s lot #’s, courthouse locations, etc.) to stop any sale of this property until I can obtain copies of the trust to understand what my rights are. I would think the faster I contact them with the fact of his death, that would at least insure I am involved in any pending sale. Also- one of the propertys is being sold BELOW tax value to one of the 1/3 parties.. which sure sounds like a scam to me!! I just want to know WHAT to file and with WHO? Most docs do not address this that I’ve found. Thanks so much !!

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