You need three things: A collector (OFC II which has a Swab & Buffer); a reader; and a LFD specific to the analyte(s) you wish to measure.
Yes you can! Add two drops to a dual LFD and you will get two readings at the same time for both biomarkers. There is plenty of sample to run about 15 tests, so you can run plenty of LFDs from one sample collection
NAN is Not A Number.  This happens with a value that is an extreme maximum or extreme minimum and so out of detection range.  It is easy to determine whether it is a minimum or maximum by visually inspecting the test line(s).  If the line is strong, the value is a low minimum; but if the test line is feint or non-existent, then your test value is a high maximum.
No. The blue dye is from the volume adequacy indicator in the stem of the OFC and is quite harmless to your sample or LFD. The reader will only scan for red colour, so the blue dye is not problematic