I would like to add a Home switch to my A axis and the easiest way to do it is to wire in series the X Home switch which is already wired to Pin 12 with the new A Home switch. Is there a problem with this setup or it has to be a separate wiring ?

that will work just fine as long as both switches are normally closed type of switches.  When either switch is triggered both X and A will light up but it doesnt matter as they will never home at the same time.  I put many switches in series like that.  You could effectively put them all on the same pin if you had to.

All my switches are NC type. Thanks fixittt for your time