(1) So long as by "duplex" you mean an actual two-unit structure (you'd be surprised...), it appears to me from the rc-c instructions that you would report it as 1c2a; you would report more than four townhomes as single family, so I don't know why this would be different.
(2) I think the important factor is not the manner in which the lien is recorded, but the seniority of the lien. The instructions indicate that if it is a junior lien, you report it as such, even if you hold the first. If you don't have an existing loan outstanding, but advance under the FADT, then you would need title work, I think, to justify reporting as a senior lien.
Hope that helps.