they are all three unique and different lenses, keep them all.
But if had to make a decision I would sell the 24-105 and the 55-250 and buy the tamron 70-300 SP VC USD instead.
The 17-55 and the 70-300 Tamron would be my choice to match the 450D or any other crop sensor. Then look at a nice macro lens like the 100 Macro 2.8 L.
Canon Powershot S95, Canon 6D,7D, Canon 40 2.8 STM, Tamron 24-70 2.8 VC, Canon 17-40 L, Canon 15-85, Canon 85 1.8, Sigma 30 1.4, 50mm 1.8, Canon 100 2.8L Macro, Canon 70-300L +Kenko 1.4 Pro 300DGX, Canon 430EX II and RS 4 Classic