X and Z homeswitches shared, Ya and Yb using own switches, is this possible?

That is simple enough. One output pin can only be connected to one signal name, but that signal name can be connected to as many inputs as you like. So I would suggest renaming your "home-x" signal to "probe-home-x" and use that for both the X home and probe connections. like this.

Try changing this to
As the error said, you have already created a signal name for your par port pin so you can reuse (eg connect it it as many times as you like. I prefer to put statements like this on two lines to keep this clear

Todd and Rodw, I will try these as soon as I am with the machine again late this afternoon.
Thank you very much for your tips!

I read up late last night on the new hal documentation, loads of possibilities !

Keep at it. One day HAL will just click and you will understand how to solve problems with it.
But the greatest feature in Linuxcnc is the ability to write your own custom HAL components. Of course it is better for ongoing support if you can use the included ones but I still have some code in my config that Todd wrote for my warning lights that I don't really understand. If I was implementing it today, I'd probably just write a component.

But Todd, you really are a HAL wizard

It works!

I went to my shop early to implement your tips. I changed the switch name and everything came alive.

I now have a self squaring gantry and I can use the probe while technically speaking I do not have enough inputs on my cheap Chinese BOB.

Thanks very much to you both Todd and Rodw. Very nice to see that people like you two are willing to help the 'virgins', keep up the good work!

I will put some comments in my .hal and .ini files and attach them to this forum thread so other novices can use the accumulated wisdom of the group.
And I am already thinking of 'reusing' all the homing switches inputs to add some real switches to control gmoccapy pins

once again thank you very much!

We were all beginners at some point. Pay it forward.