2 04's and 2 key fobs

It depends. A fob has 3 "parts". First is the removable mechanical key- that's almost certain to be different between the two cars. Second is the immobilizer transponder- that's a rfid chip in the fob case that works in the dash slot. You can use techstream to add each fob to the other's transponder ecu (so long as you don't exceed the max number of keys- each can have 5 in memory- may need to erase some). If you do that and have a spare mechical key made to unlock the door, then you can start & drive the car.
Last is the keyless entry part- the piece with the buttons and needs a battery. IF both cars are not SKS (fobs have black toyota logo on back and no black button on outside front door handle or on tailgate), then I believe you can just add each other's remote fob per the service manual procedure.
If one car is SKS (silver logo on fob with buttons on car) and one isn't, then there is no way to make keyless remote functions work.
If both cars are SKS then you CAN add each other's fobs, but you need to go to a questionable website and buy tokens to use a toyota "seed code calculator" there to access the smart key ecu and add used SKS fobs to a car.

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