I just “discovered” a b’ferush Ohr Ha’Chayim in Parshas Kedoshim 20:9 that says:
“when a son curses his Father, then he is also cursing his Mother together with the Father, and the same the reverse (when cursing the Mother, the father is also being cursed) because they are one guf, as Chazal say “Ishto k’gufo” and therefore what is done to one is also done to the other”
Hence we see that Ishto k’gufo works both ways! (Don’t you love the Bar Ilan Program – I have the entire Torah literally at my fingertips!!)
Although this seems b’stira to Tosfos in Ksubos 2b, which I need a lamdon or lamdonis to answer!