How might one fly from KRYN to SDRS in a de Hallivand DHC-6 Twin Otter?
I would recommend that you go to https://skyvector.com/ and create a flight plan.  It isn't too difficult, just click on "Flight Plan" in the top left corner and you should be able to figure out the rest.  

You obviously have some familiarity with ICAO airport identifiers, simply look for airports along the way that will keep you under a 886.7 NM leg length, and enter them one by one to build your route.  I would use a cruising speed of around 150KIAS based on a quick Google search of Twin Otter performance.  The website will calculate the times for each leg based on this airspeed.

As far as researching suitable airfields that can provide fuel and other services, that will take quite a bit of additional work.  I don't have a handy reference for you, but you could start by searching for World or Latin American Airport Directories.  I wouldn't expect anyone here to do all that work for you and post it as an answer.  If you have any detailed questions as you go don't be afraid to ask. 

Regarding your questions about avoiding immigration authorities, that's up to your fertile imagination to come up with fictional scenarios.  There is no aviation specific way to answer this, and most people would be hesitant to recommend methods to circumvent the law.