For context: Person A brings up something about a club they are in, to which person B wonders whether it is a problem for person A. A third person (female, usually speaks formally) then chimes in, referring to person A:
I think the first part is a sentence ending in 「なのです」, with 「です」 becoming 「だ」 for 「と臨海する」, but I can't figure out what the 「な」 between these two parts means. Without it, I would loosely interpret the sentence as something like
[A] would not be a member of the club if it was a problem
But I am not sure whether the 「な」 carries some extra meaning I am unaware of. Is it something like a prohibitive form? Is it a variant of 「ね」? Or am I parsing the sentence wrong in the first place?