The checks are made out to the "estate of": they are not made out to the trust. You can't use the trust bank account to deposit or cash checks which are not made out to it, any more than you can cash checks made out to your neighbor or a coworker, not you. The bank cannot deposit or cash "estate of" check without their being an estate account. And you can't even endorse the checks over to the trust because money payable to an estate becomes estate property and therefore must go through the probate (or possibly your state's "small estate" shortcut) process.Either get the letters testamentary and follow the bank's instructions regarding checks payable to an estate or else see if whomever wrote these checks can and will void them and reissue checks to the trust.