You should in general prefer to give people as much credit as possible. in AI/ML we have the astrik of "equal contribution" which can be used to make N authors technically "first author".
Yes but you'd still cite the paper as "as shown in FirstFirstAuthor et al (2024)" which rather defeats the purpose. And citing as "FirstFirstAuthor and SecondFirstAuthor and [...] et al" is both impractical and petty.
Which is what caused the whole "race to first authorship" mentality in the first place.
No, you cite the very first author only. The "multiple first author" stuff is for when you talk about your paper to others.