no option to home just Y axis on gantry with 2 Y motors

Thinking out loud:

What if I made two home buttons - one for Y1 and one for Y2 and then called them out in the vcp HAL file like this?

and

Or is that just wishful thinking?

I think the halui.joint.N.home pins for y1 and y2 should be connected to the same button so that it's not possible to activate them independently. I had tested it in a simulation and it was working there. I didn't look through your configuration files to see if I could find your error.

Would it help to add a kinstype=BOTH callout to my INI file?  I'm assuming that's safe to do since my config has it so that nothing actually moves when it homes.

Is the error and failure to start LinuxCNC because of the homing thing or something about the formatting of the halcmd it's trying to run for gladevcp?

I just noticed I had the "HALUI = halui" line in my INI file's [HAL] section commented out.  Should probably uncomment that since the VCP HAL file is calling out halui pins.  

I uncommented the "HALUI = halui" line in the INI file's [HAL] section.  That had no effect on the error message, but was something that needed to be done anyway.

Then, I added "kinstype=BOTH" to the end of the "KINEMATICS = trivkins coordinates=XYZY" line in the [KINS] section.  That got rid of the part of the error message that said:

But the other parts of the error were still there (the warning about forward kinematics handling duplicate coordinate letters and the GladeVCP command error).  Is there something wrong with the line that calls out GladeVCP in the INI file's [DISPLAY] section?  It currently says:

I might be wrong and am too lazy to check the docs but I have a feeling shared joints must start with -1 in the ini file and you have used -2. Try changing that

From section 8.3.6.10 of the 2.8.2 documentation:

"The initial HOME_SEQUENCE number may be 0, 1 (or -1). The absolute value of sequence numbers must increment by one—
skipping sequence numbers is not supported. If a sequence number is omitted, HOME ALL homing will stop upon completion
of the last valid sequence number.

Negative HOME_SEQUENCE values indicate that joints in the sequence should synchronize the final move to [JOINT_n]HOME
by waiting until all joints in the sequence are ready. If any joint has a negative HOME_SEQUENCE value, then all joints with
the same absolute value (positive or negative) of the HOME_SEQUENCE item value will synchronize the final move.

A negative HOME_SEQUENCE also applies to commands to home a single joint. If the HOME_SEQUENCE value is negative,
all joints having the same absolute value of that HOME_SEQUENCE will be homed together with a synchronized final move.
If the HOME_SEQUENCE value is zero or positive, a command to home the joint will home only the specified joint."

My four joints have HOME_SEQUENCE values of 0, 1, and -2, which meets the first two rules.  The Y1 and Y2 joints having a negative value may be unnecessary since they're not actually moving during homing.

Kins type=both should not be necessary nore would I advise adding it. I didn't have it in my simulation. Adding it will give you access to joint mode and you really don't want the ability to jog the y joints independently.

Looking at your ini file. I'm not sure if it matters but you may want to try moving the [JOINT_3] so that it is after the joint 2 section.

How you have the home sequence with 0,1,-2 is perfectly valid and isn't a problem.

I was able to get LinuxCNC to open without error and show my custom panel.  See this thread for details.

But now I have new issues.  Once I turn physical and software e-stops off and toggle machine power on in the software, I can jog X and Z, but if I try to jog Y, I get the following error:

"Homing is REQUIRED to jog the requested coordinate because joint (1) home_sequence is synchronized (-2)"

If you press the Home Y button (which you can only do at G53 Y0 since you can't jog it anywhere), it will show the little homed icon (see attached pic), so it's not totally non-functional.

If you Home All, then you can jog the Y axis.  But, if you press the Home Y button after homing all, it gives the following error:

"must be in joint mode to home"

Any ideas?