Here are more logic-like rephrasings of the sentences, which should be easier to translate into first order logic.
1. This means that for anyone $x$ (we'll assume variables range over people), if $x$ is a gentleman or $x$ is not a fighter, then $x$ is a pacifist.
2. For all $x$, if $x$ is a fighter, then if $x$ is a pacifist then $x$ is not a gentleman. More simply: for all $x$, if $x$ is a fighter and $x$ is a pacifist, then $x$ is not a gentleman.
3. I take this to mean: There are $x$ such that $x$ is a member and ($x$ is a fighter if and only if $x$ is a fighter).
4. Not: for all $x$, if $x$ is a member then $x$ is a fighter.
Can you symbolize these, using predicates $Gentleman(x)$, $Fighter(x)$, $Pacifist(x)$, and $Member(x)$?