How does homing work with a gantry XYZ system (Y and Y1 joints)?

I'm new to CNC as a whole and still in the learning stages, reading all the HAL tutorials, configuration guides and other linuxCNC documentation.   I'm well into the build of the hardware for my plasma machine which will be an X gantry over a two motor Y axis (Y and Y1 joints).  I will have home switches on all 4 joints and a stepper motor driven system.   I have a Mesa 7i76e based controller and I'm playing around with making configurations and testing things.

The documentation, tutorials and all are wonderful.  I'm learning a lot.  However something has been hard for me to wrap my head around.  I'm sure it's elementary and I'm just not getting it.  Could someone give a basic explanation (or point me at an primer) on how the homing sequence works with an XYZ gantry machine when there are two Y motors (Y and Y1 joints)?   The system should be self squaring when both Y and Y1 are homed but not quite sure how this happens without twisting the machine apart.

My basic understanding (certainly still full of holes) is each joint will go through a homing sequence when triggered.   However how is this resolved with the Y and Y1 joints?  If only one of the Y joints moves that's obviously not a good thing with the stepper for the other not moving.    Lots of things would break.  

Perhaps both Y and Y1 joints simultaneously move to home the Y axis?  Let's assume there is a slight out of square.  Then it seems indeterminate which home switch (Y or Y1) will trigger first.  Or does the homing sequence Foy Y somehow knows there are two joints and stops moving the associated joint motor for which switch triggered while the other keeps moving until that joint's home switch triggers as well?  Then both back off and go through the latch sequence in the same manner?  Finally both move same distance to final home position? 

Again, apologies if this is a silly question.   I have read plenty on setting up and configuring the machine, including the Homing Configuration docs page, but nothing I've found answered this question about Y and Y1 for me.  (if it's there I missed it)

Thanks!

-Dave

Yes, on homing,  the first joint (Y, Y1) to hit a home switch simply stops and waits for th eother side to catch up. When they both have got to the sensor, the rest of the homing sequence is completed in unison (that is the little dance to accurately sense the edge of the trigger).
Finally, the home_offset is applied to move the motors to their final position. If this point is slightly out of square, you just need to change the home_offset for one of the joints. From memory my machine has 2mm difference in offsets each side.

Awesome thanks Rod. Even as I typed the question I thought that has to be how it works. Appreciate the confirmation. Thanks for the tip on the home_offset per joint. I was thinking I'd have to do some tricky adjustment in the switches to square it. That's MUCH easier!

Cheers