The estate's lawyer, whose fee for this work typically runs $800 to $1,500, usually handles confirming these documents alongside settling any outstanding debts of the estate, since a buyer's lawyer will require proof that the person signing the sale actually has the legal right to sell the property.
In some cases a lawyer can list the property for sale while probate is still underway, but closing generally has to wait until the court has granted the executor authority, so starting the legal process early keeps the market timeline and the legal timeline moving together.
Getting these documents lined up before you list is what keeps an accepted offer from stalling. Get your hand-reviewed valuation from Joel Dyck.