Consider the word "childish". When we say it's a childish behavior we mean that it's a childlike behavior or the behavior is similar to a child. So in both the following sentences you are right about the meaning of Name + "-ish" construction
He is a nice enough boy - rather Jimmy Olsen-ish I thought. (Olsen-ish = Olsen like or similar to Olsen)
She has an unreal figure, rather Barbie-ish in its proportions! (Barbie like or similar to Barbie)
Here is a usage note from dictionary -
- (a suffix) used to form adjectives from nouns, with the sense of “belonging to” ( British; Danish; English; Spanish ); “after the
manner of,” “having the characteristics of,” “like” ( babyish;
girlish; mulish ); “addicted to,” “inclined or tending to” ( bookish;
freakish ); “near or about” ( fiftyish; sevenish ).
- (a suffix) used to form adjectives from other adjectives, with the sense of “somewhat,” “rather” ( oldish; reddish; sweetish ).
Now come to the usage of "rather" in this context -
Rather - [AS SUBMODIFIER] To a certain or significant extent or degree:
- She’s been behaving rather strangely.
- He’s rather an unpleasant man.
Now I am going to write the meaning of your sentences -
He is a nice enough boy - rather Jimmy Olsen-ish I thought. = He is a nice enough boy - almost like Olsen.
She has an unreal figure, rather Barbie-ish in its proportions! = She has an unreal figure, almost like Barbie in its proportions!
Hope it helps.