I did the same thing with my parents, mostly because they’d just say “quarter after” but would never say any number. If you made a word cloud of everything I’ve ever said in my life, “after what” would be gigantic in the center with every other word tiny around the edges.
You don’t need a separate account to play Leagues or any other temporary game modes. You are correct however that you do need to pay a separate membership for each character unless you’re okay with that character only being able to do F2P activities.