Character Analysis
Awkward Ancestor
When the kids see Grandpa as they pull up at Fablehaven, he "wore a stubbly white beard. He was dressed in faded jeans, work boots, and a flannel shirt" (1.68). Grandpa is nice but a little awkward: he looks "politely uncomfortable" (1.96) when left alone with the kids for the first time, and he confesses to Kendra's mom "I'm out of practice with children" (1.40). Gee, really?
And that seems to be the case, since Grandpa doesn't even see it coming that the kids are gonna disobey his orders to not explore the forest. He tells them that he intends to enforce the punishment he'd promised if they were disobedient, saying, "'All the same, a rule is of no value unless the punishment is enforced. You will have to stay in your room for the rest of your stay'" (4.136). Bummer, right?
But Grandpa is fair, too, since he's open to the idea that Kendra proposes, with a reduced punishment contingent on good behavior: "'You will spend tomorrow confined to the attic […] Break any of my rules again, and you will not leave the attic until your parents come for you'" (4.154). That's still kinda harsh, but at least he's open to compromise—and given the fact that his rules are pretty much a matter of life and death, it doesn't seem ridiculous to err on the side of caution.
Secret-Keeper
Grandpa's not always honest with Seth and Kendra, which leads to some problems. When he first tells them not to venture into the forest, he says it's because there are ticks out which could give them Lyme disease. When the kids do go into the forest, he changes his story, saying:
"On my land, I provide refuge for some dangerous animals, many of them endangered. […] My preserve is a secret. I have all the necessary licenses, but if my neighbors complained, those could be revoked." (4.128-130)
Hey, Gramps—if Lyme disease didn't deter these kids, it doesn't seem likely that dangerous animals will. Or at least, not for long. After the kids drink the milk though, he finally comes clean with them about what Fablehaven is. He tells them:
"I wanted to protect you from the truth about Fablehaven unless you sought it out for yourselves. It is not the kind of information I wanted to thrust upon you. That is the truth. What I'm telling you now is the truth. You'll have ample opportunity to confirm my words." (5.130)
And with all the magical adventures that follow, the kids can see that Grandpa's finally telling them the truth… mostly, anyway.
Then there's Midsummer Eve. Which Grandpa warns the kids about, like, a ton. He gives them very explicit directions, saying, "'You will be in bed at sundown. You will wear earplugs. And you will not arise until sunrise dispels the horrors of the night'" (9.45). What he doesn't tell them, though, is that they could accidentally let evil forces into the house by opening a window—which is exactly what happens. So despite his clear instructions, apparently he should've been a bit clearer. Grandpa's clearly not used to dealing with strong-willed kids like Seth.
Grandpa is also concerned with keeping the peace on the preserve. After Seth's incident with the vengeful fairies, Grandpa says, "If you have learned to be more careful and compassionate in the future, and to show greater respect for the inhabitants of this preserve, then at least some good came of all this" (8.203). Now that's optimism right there, for you.
Funny thing is, some things are secrets even to Grandpa. He tells Kendra, after all the stuff with Bahumat goes down, "I am caretaker of Fablehaven, and I know little about the artifact save that it is hidden somewhere on this property" (19.70). Wow—it kinda blows our minds that even the guy in charge of the whole place doesn't know everything about it. But it's good that he's telling Kendra all this, since he's grooming her a bit to take his place later in life.