This is a great thread. The Visconti-Sforza deck is really worth studying.
"A bon droit" is still used in French today - it means "with good right". That is, it is something correctly presumed, although not necessarily stated explicitly.
Francesco Petrarch suggested this motto for Gian Galeazzo Visconti when he was Count of Pavia. It would seem to mean that Gian Galeazzo's presumption of ruling Milan (which his uncle at that time held) was "with good right". Gian Galeazzo was the most direct in line for the succession, and would betray his uncle Bernabo to achieve domination of all of the Visconti lands in 1385.
"A bon droyt" etc. are just different ways of spelling it. In gothic writing, it is easier to see a "y" than an "i" before a "t".
"Amor myo" can be modernized to "amor mio", and means "my love". So the Two of Cups in the Visconti-Sforza deck already meant Love!