In this sort of puzzle, the author is trying to muddle you. So focus on one fact at a time, and see what you can work out!
“If you gave me three of your sweets,” sighed Josie, “We’d each have the same amount.”
“True,” agreed Susie. “But if you gave me two of your sweets, I’d have twice as many as you, which would only be fair, as I’m twice as old as you.”
“That’s not how it works,” said Mum to Susie. “By your logic, you ought to get three times as many sweets as Ellen, just because she’s two years younger than Josie. And just think how many sweets I ought to get!”
How many sweets does Josie have, how many does Susie have, and how old are the three girls?