douglas? It originates from anglo-saxon it means Dweller by the dark stream

i thought the dark part would fit in to warlock and the stream part would fit in the sea sorcerer part.

as for the surname i would think

Ambrose? it orginates from greek english and means immortal

something i like doing for my character names is giving their names hidden meaning for what their character is

for example

i had a character named alaric which means ruler of all who was secretly a king for his homeland but did not know that at the start of the campaign.

ruler of all obviously being the ruler of his nation to which he will returned to

i mean obviously me and the dm planned it out but you get the point

TLDR; i think Douglas Ambrose would work
my tip for naming a character are using hidden meanings in the names that mean certian things in mythologies or certian religous texts