There are two reasons why this may not work.
1. Although each channel can sink 500mA in isolation, the chip cannot sink much more than this in total. It would quickly overheat and fail. Even small motors can require large current for a short time when they start up. You need to measure the "Stall current" of your motors.
2. ULN2003 channels can only sink current. They cannot source it. If you motors only run in forward direction and never reverse direction, then ULN will work for that. But if you need forward and reverse, the ULN is not suitable, you need to build an "H-bridge" and ULN cannot do this by itself. Maybe if you have some pnp transistors or p-channel mosfets, you can use these combined with ULN to build an H-bridge.