Some of those voltages likely have an easy explanation: DMM's can cause an issue when measuring voltages on the inputs of some ICs if there is an internal resistance present between your leads - what happens is the leads themselves act as a voltage divider and end up reducing the measured voltage (iow, the act of measuring affects the voltage). I've had this very thing happen before on one of the multimeters I owned. I would make sure you have used a 1M resistor on R4 and not something like 10M, but I think the former explanation is the likely case.
The gate voltages on the FETs could come down to individual specs on the devices themselves, whether its their VGS ratings or some other spec. The FETs are being used as variable resistors here so as long as your octaves are triggering then I would not be concerned.
IC7 pin13 is a little more concerning. That pin is untied to anything. So there are a few possibilities here: 1) I measured that pin incorrectly and there is some internal resistance between pins 13 and 14 in the actual IC which would cause a reading of VC there 2) there is continuity between those pins either in the traces on your board or via a solder bridge or 3) you have a bad part. What I would do there is unplug the circuit, remove IC7 and if you have a continuity checker, test pins 13 and 14 in the socket to see if there is a connection. If so, check the traces and pads underneath for a board error or solder bridge. In the end, it may not matter if there is because like I said pin13 is not used for anything. As long as your IC is not getting really hot then you are probably fine.
