The tickets for both of her brothers will cost her $10 * 2 = $<<10*2=20>>20.
To buy tickets for all of them, it will cost Isabelle $20 + $20 = $<<20+20=40>>40.
Between all of them, they have saved a total of $5 + $5 = $<<5+5=10>>10.
Since they have already saved $10, she needs to earn an additional $40 - $10 = $<<30=30>>30 to afford the tickets.
Since she makes $3 per week, it will take her $30 / ($3/week) = <<30/(3)=10>>10 weeks to save enough money for all of the tickets.
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