Form 5s only transfer ownership to the beneficiary upon the disposition of the assets of the trust.
Transfer to successor trustees doesn't require a Form 5 transfer, as the trust still exists, and would still own the suppressor. The trustee could still use it, depending on your state's laws on self-dealing.
Since your beneficiary is likely one of you guys (hopefully the one who wants it), it should transfer out tax free on a Form 5 with the end of the trust. I would think that if the wrong guy is the sole beneficiary that would suck, as you'd have to do a taxable Form 4 transfer to the other guy if he wanted it.