Anything NFA that you own through the trust is still yours, your family can't borrow it so I wouldn't let them go to the range without you if that's what you're planning. The ONLY way to have multiple users/owners is through a Corporation. Not even a joint trust works, I have the NFA's letter on the matter.
If you die your heirs don't pay a transfer tax, its done on a Form 5. I don't know anything about inheritance taxes.
http://www.atf.treas.gov/forms/pdfs/f53205.pdfYou can put whatever in a trust but its no more protected from confiscation as far as I know. If its made illegal and judged contriband by stupid democrats, the NFA registry is the what and where for NFA confiscation, sorry. As to your normal title one firearms, there isn't a big registry for them so in order to get the who and where they'd have to visit gunshops for the 2475s (yellow forms). Guns bought from individuals and guns shows can't be traced that way.
Personally I wouldn't worry about confiscation, the US would be the hardest country in the world since we have the most guns in private hands, and a few Waco style standoffs would make most democrat voters loose interest.