No, occupants of the foreclosed home cannot select the Realtor. Banks have their list of REO Realtors they work with.
Cash for keys is a way for homeowners in foreclosure -- or for tenants who are victims of foreclosure -- to receive cash in exchange for surrendering the keys and vacating. Banks generally reach an agreement with the occupants of a foreclosed home, which stipulates the home will be left in good condition and cleaned. The agreements typically set forth a specific date that the home will be left vacant. Do not try to extort the bank or the offer might be withdrawn. Be pleasant, courteous and reasonable.
This is a stressful time for all involved. It's important to be cooperative and solution oriented.