I think The Oatmeal has an answer to just about everything in life, including this;
Based on that, this is my understanding:
1. One of my sisters' friends is an actress.
You have multiple sisters, at least one of them possesses several friends, one of those friends is an actress.
2. One of my sister's friends is an actress.
You have a sister who possesses friends, one of those friends is an actress.
The distinction is that in example one you have more than one sister, in example two you only have one.
Those were my initial interpretations, but as you can see, there are other meanings to consider, too.
It's easier to say, "My sister's friend is an actress."
How many sisters do you have? Does it matter? How many friends does she have? Which friend?
You could always say, "My sister Betty's friend is an actress." Or, "My sister Betty's friend Sarah is an actress."
Most anything is fine with me, except for the common mistake of using I instead of me. "My sister went to the play with Betty and I." That makes me cringe.
Rewriting a sentence is always a good practice for me, especially if it's not clear or is awkwardly written.
Misuse of pronouns is very common in daily conversations, as I indicated in my other examples (reflexives). I can tolerate some verbal grammatical errors, but I'm quite picky when it comes to writing.