"He seemed to smile" sounds like he smiled right at that moment. "He seemed to be smiling" sounds like he looked that way all along. But this must have been the way people talked (or at least wrote) back in the 1800s (when I think "Wuthering Heights" was written. I also wouldn't say "I could not think him dead", but reading an old classic like this it sounds perfectly okay. A more modern way to say it might be "I couldn't believe he was dead" or "He certainly didn't seem dead".
It would be grammatically correct to say "I think him a genius", but it is old-fashioned. These days people would probably say instead, "I think he's a genius".
It would be grammatically correct to say "I think him a genius", but it is old-fashioned. These days people would probably say instead, "I think he's a genius".
I think Kinsao is right. "I think him a genius" isn't the way people would say it in modern society, but it's grammatically correct. It's the way you might see it written in books sometimes. Maybe this is another British/American thing?
be smiling gives a connotation of he was smiling and is continuing whereas seamed to smile is that he began to smile. It's the same thing either way in this context.