This is the worst kind of puzzle, in the company of "There's a dead man in a cabin in the woods with items x, y, and z. How did he die?". The "correct" answers are completely arbitrary and the rules change as it goes along.
I like it. It's more a game of psychology than logic or reasoning - you need to get into the author's frame of mind to come up with the same solutions he did.
By now you may recognize that each hint uses letters preceding the current letter, therefore use that to guide you on a new answer. After all, it's a hint for a reason :). So for dad, what can you do with the "d" to make it somehow an "e"?
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