Oh boy - I'm also not a trust accountant or attorney, but my husband and his brother had a long, drawn-out dispute with their aunt over their grandparents' estate. Their mother had died before their grandparents did so they inherited their mother's half of the estate, which was sizable. The aunt was partially disable and not of sound mind but the grandfather left her as trustee anyway and she botched much of the transactions, which was all done out of state. She basically did what your siblings seem to be doing, which was to make unilateral decisions on what to give them and what to keep for herself - despite clearly written will and trust documents - with no accounting to back things up.
At the end of the day, they ended up needing to hire an attorney and have the attorney go to court for them (they were allowed to participate via phone) and the first order of business was a final accounting of the value of all of the contents of the trust at the date of death - including real estate, stocks, other investments, etc. - and at the dates of disbursement for the items that had already been disbursed.
With your own siblings it may be hard to play the lawyer card, but I think that you should consult with an attorney in the state in which your father died and see what they say. Laws vary much from state to state but at the end of the day, proper settlement of an estate includes a transparent and fair accounting of the contents of the estate and you are totally within reason to ask for that.
My grandmother passed away in January and the uncle who is handling the settlement of her estate has been nothing but transparent and upfront about everything. He has provided my dad (and his 6 siblings) with copies of statements of everything, they all discussed the value of the home before accepting and offer for sale and are clear on what the proceeds will be and how they'll be divided, and everything is in order to settle.
Sorry for the loss of your dad and that your siblings are being less than transparent.