Isiah is interesting to Horace as one might observe some sort of animal in the wild. But he is civil, because you never know when you'll need a favor from a werewolf.
While Horace was in India, he rarely kept in touch with those back in England (although others who were also there might've mentioned him in their correspondence), so I rather like the idea that Horace didn't know of the elder George Edgar's death. They might've been acquaintances, since Horace is the type that would humor stubborn fools like George Sr and doesn't go around advertising his alchemical studies.
Alchemy is rather like glorified chemistry and at least in Horace's mind, a science. Perhaps... Horace might need to hire Philip as an assistant?