Jack's love for his grandfather is absolute and unconditional. He does not see Grandpa's dementia as a reason to love him less, or to hand him over to strangers.
Walliams treats Grandpa's condition with honesty and warmth. The confusion and the sadness are real, but Grandpa's essential self — his bravery, his warmth, his love of flying — remains intact throughout.
Miss Swine exploits elderly people in her care. The novel is clear that this is monstrous and should be stopped.