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

That sounds like a PITA.  Could a "Home Y" button be added with GladeVCP?  It would need to (1) zero the G53 Y position and (2) mark that axis as homed.  Which doesn't seem impossible since Axis does that to the Y axis (along with the X and Z axes) when you press Home All.

Yes, to home a gantry axis by itself you can use the Halui pins "halui.joint.N.home" for all of the joints involved in the gantry axis. Simply net those together with the hal output pin from a VCP button or a real button. For example:
 

Cool - I will give that a try.

I created a UI in Glade 3.8.6-1 and saved it as "dbotos_laser_2_8_vcp.ui".  It has a button is there for homing Y and I also threw in a meter for percent full power of the laser.

I created an associated HAL file named "dbotos_laser_2_8_vcp.hal" and put the line in there suggested by Todd (with a modification for the button id).  I didn't put anything in there for the meter yet.

And, I modified my INI file as follows:

In the [DISPLAY] section, added:

In the [HAL] section, added:

When I tried to run LinuxCNC with my dbotos_laser_2_8 config, it gave the following error:

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.