Obviously you know what pass and fail mean.  Inconclusive means the examiner cannot make a decision.

More clarification is needed regarding the circumstance your husband is in. I am assuming that a government authority ran the polygraph prior to placing the nephews in your household.  

Based on the inconclusive result, what was the governmental authority placement decision? 

If they are denying the placement based on the inconclusive result, request another polygraph. During the interim, have your husband learn countermeasures.  Download the book on this site, The Lie Behind the Lie Detector.  

If they refuse to provide another polygraph all hope is not lost. Seek a private polygraph exam and pass it (countermeasures). Use the result of the private test to re-approach the government agency as proof of your husband's innocence. 

Insofar as finding a private polygraph examiner, just look in the phone book. Although your first inclination may be to look under astrology, witch doctors, etc., look under polygraph and/or private investigators. 
 
You should also contact an attorney for other legal avenues and advice. 

Good luck!