We're a one e-reader household atm, if my husband in the future decides he wants an e-reader then we'll address it at that time as to which one is the best device for him.
Disney do you and your mom share books? If so unless you want to resort to 3rd party tools you need to stay with compatible readers if you read books that aren't considered part of the public domain.
When the time comes for me to replace my K2 if it's still functioning I most likely would give it a family member or friend that doesn't have an e-reader (assuming by that point my husband has his own e-reader
).