Only one vend motor works and 1 just hums and the last one doesn't work at all.
There's the main question answered. So before you get too much deeper trying to trouble-shoot, you'll need two motors...
What I suggest is focus on the vend column that has a functioning vend motor and get this vending properly so you can use if as reference for the other non-working vend columns... The real hurdle will be trying to find vend motors...