What should I do with the money I collected for my daughter's surgery, which was then performed for free, and is it permissible for me to use it to treat the child's grandfather or for other purposes, knowing that we are from the Ashrāf?

If the money gifted to you was for the purpose of covering the expenses of your daughter's surgery, then the givers must be informed that it was not spent for the stated purpose. If they permit you to keep it, then it is yours. If they do not permit it, then they have the right to reclaim it.

However, if the gift was absolute, then you own it upon taking possession, and you are free to dispose of it. It is permissible for you, whether it was a gift or a voluntary charity. This is the view of the majority of scholars.