"Each society has its laws."
Translation:Cada sociedad tiene sus leyes.
while true, as Casiquire says, that it doesn't say "its own", that's implied in the meaning. (unless its laws are someone else's and they've stolen them.) i find that Duolingo stresses learning somewhat specifically (and that's good for learning details), but when you are actually communicating with someone, your translations can be a little looser and still be plenty accurate enough for the communication. yours is a good question.
From my understanding, reglas and leyes differ in the sense that leyes are written codes of conduct with legal consequences when broken, where as reglas are broader and suggests a rule of conduct/behavior.
Here's the link explaining the difference between reglas, leyes and normas: https://www.slideshare.net/Carlosdu/ley-regla-y-norma
1st: it is indeed sus. Those possessive adjectives agree with the noun that follows them, not with the person/people who possess the noun. So even though it's saying "its" which sounds singular, use the plural sus to agree with leyes.
2nd: 3rd person tiene instead of 2nd person tienes.