Sally has one sister (apart from herself).

Each of her 3 brothers has exactly two sisters. Since the brothers share the same sisters, there are only two sisters in total—the two sisters are Sally and her one sister. Hence, Sally has one sister.

Let me work through this step-by-step.

Sally has 3 brothers.

Each of Sally's brothers has 2 sisters.

Since Sally is a girl, she is one of the sisters that each brother has.

If each brother has 2 sisters total, and Sally is one of them, then there must be 1 other sister besides Sally.

Therefore, Sally has 1 sister.

Here are five jokes, each with a different punch‑line and premise:

1. Why did the scarecrow win an award?
   Because he was outstanding in his field!

2. I told my computer I needed a break, and it said:
   “You seem stressed—please reboot.”

3. What’s orange and sounds like a parrot?
   A carrot.

4. Why don’t scientists trust atoms anymore?
   Because they make up everything.

5. I asked the librarian if they had any books on paranoia…
   She whispered, “They’re right behind you.”

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How many are unique?
All five jokes are distinct from one another, so there are 5 unique jokes.

Here are 5 jokes:

1. Why don't scientists trust atoms? Because they make up everything!

2. What do you call a bear with no teeth? A gummy bear!

3. Why did the scarecrow win an award? He was outstanding in his field!

4. What do you call a fake noodle? An impasta!

5. Why don't eggs tell jokes? They'd crack each other up!

All 5 jokes are unique - each one has a different setup and punchline with no repeats.