Vince you have already stated your loophole; 'someone is pressued to promise something'. The does not count as a promise as i think a promise is when you promise to do (or not do) something that YOU personally WANT and think you CAN do for someone; it is not something you agree to under pressure. (sorry, i don't know if that made much sense).
I do agree that promises should not be easily broken, but as Abby said; a promise is NOT the law. It is NOT an obligation.
As for conflicting promises; keep the more important promise; the one that does the most GOOD.
As for if you have made a promise to someone who has passed away, ONLY keep that promise if it benefits someone and/or you want to keep the promise in memory of the person (IF they are a good person - and we know he wasn't).
take care xxx