Facilius eis persuasit quod undique loci natura Helvetii continentur; Quod in this case is “because” so I guess that is why continentur is in the subjunctive but I thought quod is a coordinating and not a subordinate conjunction.
Continentur is indicative.
I’m not sure I understand your question about quod. How would you translate the sentence?
It is indeed indicative. I can’t imagine what I was thinking. As for my translation: He easily persuaded them because the Helvetians are surrounded on all sides by the nature of the place.