I can't explain in title.

I was writing a song with a dotted-eighth-and-sixteenth swing on two eighth notes. And I was hoping to have someone start on the upbeat before a measure and was wondering if I had to notify the instrumentalist that it is only a sixteenth, and if so, in what way?

Also how can I imply a fermata without putting a fermata, I don't want it to be taken to heavily or for the singers to treat it very differently, it's basically supposed to be a one note 'rall.'.

As for the fermata that's maybe not a fermata, I just did a concert with a whole bunch of french music and there were quite a few fermatas that were marked with text above them as either "court" (short) or "long" or "tres long" (very long).  The Durufle "Requiem" in particular never has anything marked as just a dim. or cres. or rit.  It's all given more precision with the addition of a "molto" or a "poco."  

You can always put an explanatory note at the bottom of the page with a little * if you want to be very specific about the treatment you want.