Which is Kraft Lawrence's familiar name, and which his surname?
I'm pretty sure "Lawrence" is intended to be his surname/family name and "Kraft" his personal name. My recollection from the anime is that he is occasionally referred to as "Lawrence-san," which while permissible for a personal name would be unusual enough to be remarked.

Moreover, he's frequently referred to as "Mr. Lawrence" by people who would have absolutely no reason to call him something cutesy like Mr. Personal-name. For example, in the Vol. 1 of the light novel (Yen Press translation), Marheit (head of Milone Trading, features in the silver trenni arc) calls him "Mr. Lawrence" on pp. 238, 243, 248, 260... pretty much throughout their interactions.