Well, learning to recognize unfamiliar sounds is part of learning a language.
If you want a clear separate pronunciation (and therefore unnatural), you can use the slow version.
No and non have different o's, the same way that 'sh#t' (/ˈʃɪt/) and 'sheet' (/ˈʃiːt/) have different sounds. An Italian taking their first steps in English would not recognize/hear any difference
Due to the complexity of the Italian verbs system, the task of learning the conjugations should be taken outside of Duolingo.
This Wikipedia page seems very informative:
It should be "no, non se la ricordano", at least that's how it's used (as a reflexive verb) if you talk about something specific. If you talk about something for example historical, like "they don't remember the times" that's when you can use it not reflexive - said my native Italian girlfriend