As you can see @ilovetaxes this has the potential to get rather complex. It could also be extremely simple too. It just depends on the type of trust. (There are four basic types of irrevocable trusts that I am aware of, and their may be more I'm not aware of.)
Basically, the first thing that "must" happen is probate on the estate. Nothing matters until probate is completed in it's entirety. Period.
If (and that's *ONLY* if) upon completion of probate, all three of you are listed as owners of the house, then what each of you do with your 1/3 share is your business. If two owners want to sell their share to the remaining owner, they most certainly can.
One thing that "MUST" be done though, and preferably done yesterday if not sooner, is to determine cost basis of the house. Is it the FMV of the property upon the passing of your father? Or is it the FMV of the property at the time it was transferred and titled to the trust? It depends on the type of irrevocable trust. This matters big time, as each of you will get 1/3 of that cost basis.
Then when each member sells their 1/3 share, any amount of gain over that cost basis is taxable income to the seller and must be reported on the seller's personal tax return for the tax year of the sale.
