Translation:They are all women.
Yes, but 彼女たち is a form of "they" that matches みんな女の人.
In English, we don't use different words to distinguish between men and women when we use "they." However, in other languages, gender does affect the third-person plural pronoun. An easy example is in Spanish, ellas is used for "they (women)" and ellos is used for "they (men)."
In Japanese, this isn't as straightforward, because there are multiple ways of referring to a group of people, and often pronouns are dropped altogether. But, for this sentence it is not redundant to use 彼女たち because that is a correct pronoun for talking about みんな女の人.
"They all are" sounds better to me, a native English speaker. I know what you mean if you say "they are all women," but it kind of sounds like you mean that what they are is [all women]. The difference is more obvious with verbs besides the copula; "They all know things" is very different from "They know all things." I know this isn't supposed to be a discussion of English, but I was very surprised to see that you thought my preferred word order was odd.