My pick was #2, however I was thinking of #5 as well. One thing that made it hard is that you seem to have the same facial expression as the people you’re photographed with which gives a similarity in most of the photos. I was put off #5 by her nose which is different from yours, but her mouth and eyes are very similar.
Seconded in every respect :).
I knew it was the one that it was. You look very similar to me.
I think #2
I did not read any other responses before posting
#1 has your exact same nose, but otherwise I got nothing.
To me, number 3 looks closest.
But there’s no obvious answer.
I’m going to guess #5. The coloring is different, but the expressions are the same. My sister and I are the same way. She’s a Winona Ryder type and I’m more a Catherine Zeta type but we smile alike, make the same gestures, and people can tell we’re sisters all the time even though we look nothing alike.
Genetics are a kick in the pants. Who was it?
Someone told me once that you can always tell family members from behind by their walk. Since he said that I’ve been staring at stranger’s bottoms, and he’s right. 
The more pictures I see, the more you look alike to me. Don’t worry about it; I have three sisters, I think we look completely different, and everyone says we look like quadruplets. We do all sound alike, though, including my mom. It was hard on the boyfriends when they start dating us; “One of your sisters or your mom called; I couldn’t tell which one.”
We should’ve known by the lack of a smile in that one!
(I’d have said #2; your noses look more similar. Shows what I know.)
My first impulse was #5, but after reexamination, I say #2. You both have the same nose, teeth, lips, and body type.
Also, it’s hard to tell, but I think #5 has different ears than you do.
Now, to read the thread and see how I did…
ETA: I guess I overthought it.
22222222222222222!!!
Oh damn.
At first I thought maybe 5 because you weren’t smiling (i.e., no need for sisters to cheese it up because you’ve taken a million pics together in your lives), but then 2’s nose made me go 222222222222.
Also, tell your dad he may want to look into the term “to cuckold.” 
I thought #4, but I am famously terrible with faces.
My wife, who is VERY visual and good with faces, picked #2.
Your Mom be wrong, but that’s to be expected- she’s too close to have a good perspective.
Number 2
I say #5. Haven’t read the thread and don’t intend to.
This thread is hilarious.
Prior to the answer being revealed, all 14 replies guessed wrong. But once the answer was posted, nearly 50% of the replies posted the correct answer!
I have three lovely sisters. One sister is a blue eyed blond with golden skin and a medium build; one is light olive skinned with near black hair and medium brown eyes who is really curvy in all the right places, one has chocolate brown eyes, brown hair, cafe au lait skin and a willowy build, and one has light reddish brown hair, amber eyes, (charitably put) a dancer’s build, and paler than pale skin with freckles.
In short, we are as unalike in appearance as can be.
Nevertheless, strangers can tell we are sisters when we go out together, for reasons which do not appear in pictures. We speak in much the same way, we have similar gestures, similar facial expressions. We also finish each other’s sentences but I suppose girlfriends might do that, too.
So it may well be obvious that you are sisters in person, whether you look alike or not.
we had more time to consider our answers?
You and your sister look extremely dissimilar. When you look at the full size version of this picture, it’s more noticeable that you have completely different eyes (yours having a more pronounced upper lid), utterly and completely different noses (yours wider, hers thinner), different lips (yours fuller and hers thinner) and different chins (yours more pointed and hers more rounded).
You’re right that when you look at the family picture, particularly the enlarged version, it’s obvious you’re all family. You look just like your father, but with your mother’s nose and coloring, and your sister looks just like your mother, but with your father’s nose and coloring.
For the record, my initial guess was #2. I still say she looks more like you than your actual sister.
Without intentionally looking at any other responses, I’d say that something about the mouth and nose make me think it’s the girl in picture #2.