it would be easier with N/C switches with a PNP open collector output
what is the part number of the proximity sensors you have ? and do you have a link to the data sheet ??
can they work when powered by the C10 BOB's 5V supply supply ??
if they have to be powered by a 12 V supply you need to limit the voltage that's applied to the C10 input to 0 to +5V
(the absolute limit for input of the 74ACT245 IC used for the C10 is -0.6V to +5.6V)
John