My dc are all into the same series. Dd1 being older discovered them first. She wanted copies herself and she got two of them for a Christmas present, and one for holiday reading last summer. The younger ones have got into the same series over the summer. Now ds wants the fourth one (we read a library copy) for his birthday soon (it is just this and an mp3 player on his list). Dd also wants to use pocket money to add to the others in the series. Ds would be allowed to read dd's but only under certain conditions (she's not reading it, he washes his hands, doesn't eat or drink near it, doesn't bend a page, sneeze near it etc etc etc).
Part of me feels that multiple copies in the same house is excessive. Another part of me reminds me how much I have enjoyed passing on MY books and sharing them with my dc. My sister didn't read much so all the books were mine. Do you ever buy multiple copies for dc?
Fortunately there will only be five in the series so it is a finite commitment. ignores all the spinoffs